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Kuwait University Chemistry Aptitude Test study materials
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Kuwait University Chemistry Aptitude Test practice questions

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Question 1English

In a chemistry lab report, which sentence uses the article correctly before a noun beginning with a vowel sound?

  1. The student recorded an hour-long observation about the reaction rate.
  2. The student recorded the observation about reaction rate quickly.
  3. The student recorded a observation about the reaction rate.
  4. The student recorded an observation about the reaction rate. Correct answer.

Explanation

The indefinite article 'an' is used before words beginning with a vowel sound, and 'observation' starts with the vowel sound /ɒ/. 'A observation' is therefore ungrammatical because the article and the following sound clash.

Question 2English

Which sentence correctly uses the present perfect tense to describe a laboratory result that is relevant now?

  1. The titration reached the endpoint, so we can stop adding the base.
  2. The titration is reaching the endpoint, so we can stop adding the base.
  3. The titration has reached the endpoint, so we can stop adding the base. Correct answer.
  4. The titration reaches the endpoint, so we can stop adding the base.

Explanation

The present perfect 'has reached' connects a completed action to the present moment, which fits a result that now allows the next step. The simple past 'reached' is possible but less precise about present relevance, while the present and present continuous do not express a completed result.

Question 3English

In the sentence 'The solution was heated until it boiled', what is the grammatical function of 'until it boiled'?

  1. An adverbial clause of time modifying 'was heated' Correct answer.
  2. A relative clause modifying 'solution'
  3. An adjective phrase modifying 'heated'
  4. A noun clause acting as the subject

Explanation

'Until it boiled' contains a subject and a verb and is introduced by the subordinating conjunction 'until', so it functions as an adverbial clause. It tells us the time up to which the heating continued, modifying the verb 'was heated'.

Question 4English

Which word is the best synonym for 'volatile' as used to describe a chemical substance?

  1. Completely soluble
  2. Easily evaporated Correct answer.
  3. Highly toxic
  4. Chemically inert

Explanation

In chemistry, 'volatile' describes a substance that evaporates readily at normal temperatures because of a high vapour pressure. Toxicity, solubility, and inertness are separate properties and do not define volatility.

Question 5English

Which sentence uses the correct preposition after the verb 'depend' in a scientific context?

  1. The yield of the reaction depends to the temperature.
  2. The yield of the reaction depends from the temperature.
  3. The yield of the reaction depends on the temperature. Correct answer.
  4. The yield of the reaction depends of the temperature.

Explanation

The verb 'depend' is followed by the preposition 'on' (or 'upon') when stating the condition that determines something. The other prepositions do not collocate with 'depend' in standard English.

Question 6English

Choose the correct plural form to complete the sentence: 'The laboratory contained several ___ of sodium chloride.'

  1. bottle
  2. bottles'
  3. bottles Correct answer.
  4. bottled

Explanation

The quantifier 'several' requires a countable plural noun, so 'bottles' is correct. The singular 'bottle' cannot follow 'several', the possessive 'bottles'' would need a following noun, and 'bottled' is a participle or adjective.

Question 7English

Which sentence correctly uses 'fewer' rather than 'less' in a laboratory instruction?

  1. Use little drops of indicator in the next trial.
  2. Use less drops of indicator in the next trial.
  3. Use fewer drops of indicator in the next trial. Correct answer.
  4. Use lesser drops of indicator in the next trial.

Explanation

'Fewer' is used with plural countable nouns such as 'drops', while 'less' is used with uncountable nouns. 'Lesser' means inferior in importance, and 'little' does not fit a plural countable noun here.

Question 8English

What does the prefix 'hydro-' mean in words such as 'hydrocarbon' and 'hydrolysis'?

  1. Heat
  2. Water Correct answer.
  3. Air
  4. Light

Explanation

The prefix 'hydro-' comes from the Greek word for water. In 'hydrocarbon' it signals the presence of hydrogen, which is a component of water, and in 'hydrolysis' it refers to splitting by water.

Question 9English

Which sentence correctly uses a comparative adjective to compare two experimental methods?

  1. Method A is efficienter than Method B.
  2. Method A is most efficient than Method B.
  3. Method A is more efficient that Method B.
  4. Method A is more efficient than Method B. Correct answer.

Explanation

For a two-item comparison, the comparative form is required, and multi-syllable adjectives such as 'efficient' form it with 'more'. The comparative is followed by 'than', not 'that'.

Question 10English

Identify the sentence in which the passive voice is used appropriately for a scientific procedure.

  1. The mixture stirred for ten minutes before filtration.
  2. The mixture is stirring for ten minutes before filtration.
  3. The mixture was stirred for ten minutes before filtration. Correct answer.
  4. The mixture stirs for ten minutes before filtration.

Explanation

The passive 'was stirred' is appropriate because the procedure focuses on what happened to the mixture rather than on who performed the action. The active forms shift attention to the mixture as an agent, which is inaccurate for a procedure.

Question 11English

Which sentence uses a modal verb that expresses the strongest degree of obligation in a safety rule?

  1. Students must wear goggles in the laboratory at all times. Correct answer.
  2. Students may wear goggles in the laboratory at all times.
  3. Students could wear goggles in the laboratory at all times.
  4. Students should wear goggles in the laboratory at all times.

Explanation

'Must' expresses strong obligation or necessity, which is appropriate for a mandatory safety rule. 'Should' gives advice, 'may' grants permission, and 'could' expresses possibility or ability.

Question 12English

In the sentence 'The residue, which was dark brown, was discarded', what is the function of the commas?

  1. They enclose a non-defining relative clause. Correct answer.
  2. They separate items in a list.
  3. They introduce a direct quotation.
  4. They mark a parenthetical interjection.

Explanation

The clause 'which was dark brown' adds extra, non-essential information about the residue, so it is a non-defining relative clause enclosed by commas. Removing it would not change the basic identification of the residue.

Question 13English

Which sentence correctly uses 'amount' or 'number' according to whether the noun is countable?

  1. A large amount of molecules was detected in the sample.
  2. A large number of water was detected in the sample.
  3. A large number of molecules were detected in the sample. Correct answer.
  4. A large amount of molecules were detected in the sample.

Explanation

'Number' is used with plural countable nouns such as 'molecules', while 'amount' is used with uncountable nouns such as 'water'. The verb 'were' also agrees with the plural 'molecules'.

Question 14English

Which sentence correctly uses a conditional structure to describe a hypothetical experiment?

  1. If the temperature is higher, the reaction would proceed faster.
  2. If the temperature was higher, the reaction will proceed faster.
  3. If the temperature were higher, the reaction will proceed faster.
  4. If the temperature were higher, the reaction would proceed faster. Correct answer.

Explanation

This is a second conditional sentence describing an unreal or hypothetical situation, so it pairs 'were' in the if-clause with 'would' in the main clause. Mixing 'was' with 'will' or 'were' with 'will' breaks the conditional pattern.

Question 15English

Which word correctly completes the sentence: 'The precipitate was ___ filtered and dried before weighing.'

  1. carefully Correct answer.
  2. careful
  3. care
  4. carefulness

Explanation

The verb 'filtered' needs an adverb to describe how the action was performed, and 'carefully' is the adverb form. 'Careful' is an adjective, 'carefulness' is a noun, and 'care' is a noun or verb.

Question 16English

Which sentence uses 'that' correctly as a relative pronoun in a defining clause?

  1. The compound, that formed, was insoluble in water.
  2. The compound what formed was insoluble in water.
  3. The compound that it formed was insoluble in water.
  4. The compound that formed was insoluble in water. Correct answer.

Explanation

In a defining relative clause, 'that' can replace 'which' or 'who' and directly follows the noun it identifies. It functions as the subject of 'formed' without adding a redundant pronoun.

Question 17English

Which sentence correctly uses a gerund as the subject of a sentence about laboratory practice?

  1. Record accurate measurements is essential in quantitative analysis.
  2. Recording accurate measurements is essential in quantitative analysis. Correct answer.
  3. To recording accurate measurements is essential in quantitative analysis.
  4. Recorded accurate measurements is essential in quantitative analysis.

Explanation

A gerund is the -ing form of a verb used as a noun, and here 'recording accurate measurements' is the subject of 'is'. The other options use a bare verb, a malformed infinitive, or a past participle, none of which can serve as the subject in this way.

Question 18English

Choose the sentence that correctly reports a scientist's statement: 'The sample is contaminated,' she said.

  1. She said that the sample was contaminated. Correct answer.
  2. She said that the sample is contaminated yesterday.
  3. She said the sample contaminated.
  4. She said that was contaminated the sample.

Explanation

In reported speech, the present tense of the original statement usually shifts back to the past when the reporting verb is in the past, so 'is' becomes 'was'. The other options contain tense clashes, missing subjects, or disordered word order.

Question 19English

Which sentence uses 'although' correctly to contrast two experimental findings?

  1. Although the yield was low, the purity was excellent. Correct answer.
  2. Although the yield was low, however the purity was excellent.
  3. Although the yield was low, so the purity was excellent.
  4. Although the yield was low, but the purity was excellent.

Explanation

'Although' introduces a subordinate clause of concession, and the main clause follows without another conjunction. Adding 'but', 'however', or 'so' creates a double connector that is nonstandard in formal writing.

Question 20English

In the phrase 'a highly sensitive balance', what is the grammatical role of 'highly'?

  1. It is an adverb modifying the adjective 'sensitive'. Correct answer.
  2. It is a preposition introducing a phrase.
  3. It is an adjective modifying the noun 'balance'.
  4. It is a noun functioning as an appositive.

Explanation

'Highly' is an adverb of degree that intensifies the adjective 'sensitive'. Adverbs can modify adjectives, whereas adjectives modify nouns and prepositions introduce phrases.

Question 21English

Which sentence uses a colon correctly in a formal laboratory report?

  1. The sample contained three impurities: sodium chloride, calcium carbonate, and silica. Correct answer.
  2. The sample contained three impurities, sodium chloride: calcium carbonate, and silica.
  3. The sample contained: three impurities sodium chloride, calcium carbonate, and silica.
  4. The sample contained three impurities; sodium chloride: calcium carbonate, and silica.

Explanation

A colon introduces a list or explanation after a complete independent clause. Here 'The sample contained three impurities' is complete, and the colon correctly introduces the list that follows.

Question 22English

Which sentence avoids a dangling modifier?

  1. Heating the solution, a colour change was observed.
  2. After heating the solution, the technician observed a colour change. Correct answer.
  3. After heating the solution, the colour changed.
  4. After heating the solution, a colour change was observed.

Explanation

A participial phrase at the start of a sentence must refer to the subject of the main clause. Only in the first option does 'the technician' perform the heating, so the modifier is properly attached.

Question 23English

Which sentence uses 'respectively' correctly when matching two lists?

  1. Respectively, sodium and chlorine were detected by flame test and silver nitrate test.
  2. Sodium and chlorine respectively were detected by flame test and silver nitrate test.
  3. Sodium and chlorine were detected by flame test and silver nitrate test, respectively. Correct answer.
  4. Sodium and chlorine were detected respectively by flame test and silver nitrate test.

Explanation

'Respectively' should follow the two lists it correlates and signal a one-to-one matching in the same order. Placing it between the verb and the first list, or at the start of the sentence, obscures which item pairs with which test.

Question 24English

Which sentence correctly uses a semicolon to join two closely related independent clauses?

  1. The reaction was exothermic; and the flask felt warm to the touch.
  2. The reaction was exothermic; the flask felt warm to the touch. Correct answer.
  3. The reaction was exothermic the flask; felt warm to the touch.
  4. The reaction was exothermic, the flask felt warm to the touch.

Explanation

A semicolon can join two independent clauses that are closely related in meaning without a coordinating conjunction. A comma alone creates a comma splice, and adding 'and' after the semicolon is redundant.

Question 25English

Which sentence uses 'comprise' in a way that is standard in formal scientific writing?

  1. The mixture comprises of three volatile components.
  2. The mixture is comprised of three volatile components.
  3. The mixture comprises three volatile components. Correct answer.
  4. The mixture is comprising three volatile components.

Explanation

'Comprise' means 'consist of' and takes a direct object without 'of', so 'comprises three components' is standard. The passive 'is comprised of' and the form 'comprises of' are widely criticised in formal usage.

Question 26English

In a chemistry report, choose the sentence that uses the definite article correctly for a substance already introduced earlier in the paragraph.

  1. A sample of copper sulfate was weighed; the sample was then dissolved in water. Correct answer.
  2. Sample of copper sulfate was weighed; sample was then dissolved in water.
  3. A sample of copper sulfate was weighed; a sample was then dissolved in water.
  4. The sample of copper sulfate was weighed; a sample was then dissolved in water.

Explanation

The definite article 'the' marks a noun that both writer and reader can identify, which is true once the sample has already been mentioned. The first mention appropriately takes the indefinite article 'a' because it introduces new information. This given-then-known pattern is standard in scientific procedure writing.

Question 27English

Which sentence uses the preposition that correctly collocates with the verb in a laboratory context?

  1. The technician insisted at repeating the titration.
  2. The technician insisted to repeat the titration.
  3. The technician insisted on repeating the titration. Correct answer.
  4. The technician insisted for repeating the titration.

Explanation

The verb 'insist' is followed by the preposition 'on' plus a gerund, giving 'insisted on repeating'. Preposition choice with verbs is fixed by convention rather than by logic, so it must be memorised as a unit. The other prepositions do not collocate with 'insist' in standard English.

Question 28English

A student writes: 'The titration was performed by me.' Which revision is more appropriate for a formal laboratory report?

  1. The titration was performed by myself.
  2. I performed the titration. Correct answer.
  3. The titration I performed it.
  4. The titration was performed by the person of me.

Explanation

Formal scientific writing generally prefers the active voice with a clear agent when the agent matters, and 'I performed the titration' is direct and grammatical. The passive version is not wrong, but the active alternative is the cleanest revision here. The remaining options are grammatically faulty.

Question 29English

Which word correctly completes the sentence: 'The solution was stirred ___ until all the crystals had dissolved'?

  1. continue
  2. continuously Correct answer.
  3. continuation
  4. continuous

Explanation

The blank modifies the verb 'stirred', so an adverb is required, and 'continuously' is the adverb form of 'continuous'. Adjectives modify nouns, not verbs, so 'continuous' cannot fill this slot. The noun and verb forms are also grammatically impossible here.

Question 30English

In the instruction 'Heat the mixture gently, and then add the acid dropwise', what does the comma chiefly signal?

  1. It separates a subject from its verb.
  2. It separates two independent clauses joined by a coordinating conjunction. Correct answer.
  3. It introduces a list of three or more items.
  4. It marks a non-defining relative clause.

Explanation

Both 'Heat the mixture gently' and 'then add the acid dropwise' are independent clauses, and the comma precedes the coordinating conjunction 'and'. This is the standard punctuation pattern for joining two such clauses. The other described functions do not match this sentence.

Question 31English

Which sentence uses 'its' and 'it's' correctly in a description of an instrument?

  1. The balance lost it's calibration, and its readings became unreliable.
  2. The balance lost its calibration, and it's readings became unreliable.
  3. The balance lost it's calibration, and it's readings became unreliable.
  4. The balance lost its calibration, and its readings became unreliable. Correct answer.

Explanation

'Its' is the possessive determiner, while 'it's' is the contraction of 'it is' or 'it has'. Both blanks require possession, so 'its' is correct in each. Confusing the two is a common error in technical writing.

Question 32English

Which sentence uses the correct comparative or superlative form when three or more methods are compared?

  1. Of the three methods, the titration was the accuratest.
  2. Of the three methods, the titration was the most accurate. Correct answer.
  3. Of the three methods, the titration was the more accurate.
  4. Of the three methods, the titration was more accurate than all.

Explanation

When three or more items are compared, English uses the superlative form, here 'the most accurate'. The comparative 'more accurate' is reserved for a comparison between exactly two items. 'Accuratest' is not a valid English form.

Question 33English

Which sentence places the adverb in the position most natural for formal scientific English?

  1. Carefully the precipitate was filtered and then dried.
  2. The precipitate carefully was filtered and then dried.
  3. The precipitate was filtered carefully and then dried.
  4. The precipitate was carefully filtered and then dried. Correct answer.

Explanation

An adverb of manner normally sits between the auxiliary and the past participle, giving 'was carefully filtered'. This placement keeps the manner closely attached to the participle it modifies. The other positions are either awkward or unnatural in a procedural description.

Question 34English

Which sentence uses 'due to' in a way accepted in formal scientific writing?

  1. The delay was due to a faulty thermometer. Correct answer.
  2. The experiment stopped due to the thermometer was faulty.
  3. Due to the thermometer was faulty, the experiment stopped.
  4. The delay was due to because the thermometer was faulty.

Explanation

In careful usage 'due to' functions as an adjectival phrase following a form of 'be', as in 'was due to a faulty thermometer'. It should introduce a noun phrase, not a full clause. The other options either misuse it as a conjunction or combine it redundantly with 'because'.

Question 35English

Choose the sentence in which the relative pronoun can correctly be omitted.

  1. The student who performed the titration received full marks.
  2. The sample that was contaminated was discarded.
  3. The beaker which broke was expensive.
  4. The method which the team adopted proved reliable. Correct answer.

Explanation

A relative pronoun may be omitted when it functions as the object of the verb in a defining relative clause. In 'the method which the team adopted', 'which' is the object of 'adopted', so it can be dropped. In the other sentences the pronoun is the subject of its clause and cannot be omitted.

Question 36English

Which sentence uses the present perfect correctly to report a result that is relevant to the current discussion?

  1. We have completed the analysis yesterday.
  2. We are completing the analysis yesterday.
  3. We have completed the analysis yesterday and today.
  4. We completed the analysis yesterday. Correct answer.

Explanation

A definite past time expression such as 'yesterday' requires the simple past, because the present perfect cannot be used with a specific finished time. 'We completed the analysis yesterday' is therefore the only fully acceptable sentence. The others either clash with the time expression or use the wrong tense.

Question 37English

Which sentence correctly uses 'whereas' to contrast two results?

  1. The first trial gave a high yield, whereas the second gave a low yield. Correct answer.
  2. Whereas the first trial gave a high yield, it was fast.
  3. The first trial gave a high yield whereas because the second gave a low yield.
  4. The first trial gave a high yield, whereas gave a low yield.

Explanation

'Whereas' is a subordinating conjunction that joins two contrasting clauses, each with its own subject and verb. The first option supplies both clauses and marks the contrast correctly. The others omit a subject, contrast unrelated ideas, or combine two connectors redundantly.

Question 38English

Which sentence uses a participle clause that is correctly attached to its subject?

  1. Having calibrated the balance, the readings were recorded by the technician.
  2. Having calibrated the balance, the technician recorded the readings. Correct answer.
  3. Having calibrated the balance, the readings recorded the technician.
  4. Having calibrated the balance, it recorded the readings.

Explanation

A participle clause at the start of a sentence is understood to share its subject with the main clause. In the correct option the technician both calibrated the balance and recorded the readings, so the attachment is logical. The others leave the participle attached to an impossible subject.

Question 39English

Which sentence correctly uses 'each' with a plural noun in a statement about replicate measurements?

  1. Each of the samples were weighed twice.
  2. Each of the samples was weighed twice. Correct answer.
  3. Each of the sample were weighed twice.
  4. Each of samples was weighed twice.

Explanation

'Each of' is followed by a plural noun or pronoun and takes a singular verb, because 'each' focuses on individuals one at a time. Hence 'each of the samples was weighed'. The other options violate either the number of the noun or the agreement of the verb.

Question 40English

Which sentence uses 'data' in the way most consistent with formal scientific convention?

  1. The datas were collected over three weeks and were analysed.
  2. The data was collected over three weeks and were analysed.
  3. The data was collected over three weeks and it was analysed.
  4. The data were collected over three weeks and were analysed. Correct answer.

Explanation

In formal scientific writing 'data' is often treated as the plural of 'datum', so it takes a plural verb such as 'were'. Keeping the verb consistently plural avoids the mixed agreement seen in some options. The plural form 'datas' does not exist in standard English.

Question 41English

Which sentence uses 'because of' correctly?

  1. Because of the solution was too acidic, the reaction failed.
  2. The reaction failed because of it was too acidic.
  3. The reaction failed because of the excessive acidity of the solution. Correct answer.
  4. The reaction failed because of the solution was too acidic.

Explanation

'Because of' is a compound preposition and must be followed by a noun phrase, as in 'the excessive acidity of the solution'. It cannot introduce a finite clause; that role belongs to 'because'. The other options all place a clause after 'because of'.

Question 42English

Which sentence uses the apostrophe correctly for a possessive plural in a laboratory context?

  1. The students' results were recorded in the logbook. Correct answer.
  2. The students's results were recorded in the logbook.
  3. The student's results were recorded in the logbook by all of them.
  4. The students results were recorded in the logbook.

Explanation

A regular plural noun ending in -s forms the possessive by adding only an apostrophe after the s, giving 'students''. The apostrophe marks possession without adding another s. The other options either omit the apostrophe or misplace it.

Question 43English

Which sentence correctly uses 'although' at the start of a sentence?

  1. Although the yield was low, but the purity was excellent.
  2. Although the yield was low, the purity was excellent. Correct answer.
  3. Although the yield was low, and the purity was excellent.
  4. Although the yield was low. The purity was excellent.

Explanation

'Although' introduces a subordinate clause that must be joined to a main clause, and a comma normally separates the two when the subordinate clause comes first. The correct option does exactly this. The others add a redundant conjunction or break the sentence incorrectly.

Question 44English

Which sentence uses the modal 'must' with the meaning of a logical deduction rather than an obligation?

  1. You must wear goggles in the laboratory at all times.
  2. The unexpected colour change must indicate contamination. Correct answer.
  3. The sample must be stored below 4 degrees Celsius.
  4. Students must submit their reports by Friday.

Explanation

'Must' can express either obligation or a strong logical conclusion. In 'must indicate contamination' the speaker is drawing an inference from evidence, which is deduction. The other sentences impose requirements on people or procedures.

Question 45English

Which sentence uses 'such as' correctly when giving examples in a scientific text?

  1. Noble gases such as helium and argon and they are chemically unreactive.
  2. Noble gases such as helium and argon are chemically unreactive. Correct answer.
  3. Such as noble gases, helium and argon are chemically unreactive.
  4. Noble gases are such as helium and argon chemically unreactive.

Explanation

'Such as' introduces examples that illustrate a preceding general category, so 'noble gases such as helium and argon' is the standard pattern. It should be integrated into the noun phrase without adding a second subject or verb. The other options scramble the syntax.

Question 46English

Which sentence uses the subjunctive correctly after a verb of recommendation?

  1. The supervisor recommended that the sample is stored in the dark.
  2. The supervisor recommended that the sample be stored in the dark. Correct answer.
  3. The supervisor recommended that the sample was stored in the dark.
  4. The supervisor recommended that the sample will be stored in the dark.

Explanation

After verbs such as 'recommend', 'suggest' and 'insist', formal English uses the mandative subjunctive, which takes the base form of the verb regardless of subject: 'that the sample be stored'. This signals a recommendation about what should happen. The indicative forms describe fact rather than recommendation.

Question 47English

Which sentence uses 'not only ... but also' with correct parallel structure?

  1. The method improved not only yield but also reduced waste.
  2. The method not only improved yield but also it reduced waste.
  3. The method not only improved yield but also reduced waste. Correct answer.
  4. Not only the method improved yield but also reduced waste.

Explanation

Correlative conjunctions require parallel grammatical elements after each part. Here 'improved yield' and 'reduced waste' are both verb phrases, so the structure is balanced. The other options break parallelism or misplace the correlatives.

Question 48English

Which sentence avoids a misplaced modifier when describing a heated flask?

  1. Heated to 80 degrees Celsius, the observation was made of the flask.
  2. Heated to 80 degrees Celsius, the flask was observed by the student. Correct answer.
  3. The student observed the flask heated to 80 degrees Celsius quickly.
  4. Heated to 80 degrees Celsius, the student observed the flask.

Explanation

A participial phrase at the beginning of a sentence must describe the subject of the main clause. In the correct option the flask, not the student, is the thing heated to 80 degrees Celsius. The other options attach the participle to an entity that cannot logically be heated.

Question 49English

Which sentence uses the semicolon and conjunctive adverb correctly in a discussion of two results?

  1. The first trial gave a high yield; however, the second gave a low yield. Correct answer.
  2. The first trial gave a high yield; however the second, gave a low yield.
  3. The first trial gave a high yield, however, the second gave a low yield.
  4. The first trial gave a high yield however; the second gave a low yield.

Explanation

A semicolon can join two independent clauses, and a conjunctive adverb such as 'however' is followed by a comma. The correct option satisfies both rules. The others either use a comma splice, omit the comma after 'however', or place the semicolon wrongly.

Question 50English

Which sentence uses the gerund phrase as the object of a preposition rather than as a subject?

  1. Stirring the solution slowly prevents crystallisation.
  2. The technician succeeded in reducing the reaction time. Correct answer.
  3. To reduce the reaction time was the main aim.
  4. Reduced reaction time improves the yield.

Explanation

A gerund phrase functions as the object of a preposition when it follows one, as in 'succeeded in reducing the reaction time'. The gerund 'reducing' is governed by 'in'. The other options place a gerund or infinitive in the subject position or use a noun phrase.