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Cambridge HSC practice questions

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Question 1Sciences (Biology, Chemistry, Physics, related subjects)

Water enters a root hair cell from the soil and passes through aquaporins into the vacuole. Which process primarily describes this movement?

  1. Active transport
  2. Osmosis Correct answer.
  3. Bulk flow
  4. Endocytosis

Explanation

Water moves down its water-potential gradient from the soil solution into the root hair cell across a selectively permeable membrane. Aquaporins provide a channel for this osmotic movement, which does not directly require ATP.

Question 2Sciences (Biology, Chemistry, Physics, related subjects)

Which pair of elements is most likely to form an ionic compound?

  1. Nitrogen and hydrogen
  2. Carbon and oxygen
  3. Sodium and chlorine Correct answer.
  4. Chlorine and chlorine

Explanation

Ionic bonding is favoured when a metal transfers electrons to a non-metal, producing oppositely charged ions. Sodium is a metal and chlorine is a non-metal, so sodium chloride is ionic.

Question 3Sciences (Biology, Chemistry, Physics, related subjects)

A cyclist travels 150 m due north in 30 s. What is the cyclist's average velocity?

  1. 5 m/s north Correct answer.
  2. 4500 m/s north
  3. 5 m/s south
  4. 180 m/s north

Explanation

Average velocity is displacement divided by time, with direction included. The displacement is 150 m north, so v = 150/30 = 5 m/s north.

Question 4Sciences (Biology, Chemistry, Physics, related subjects)

A molecule binds to the active site of an enzyme, and its inhibitory effect is reduced when substrate concentration is increased. This is characteristic of which type of inhibition?

  1. Irreversible inhibition
  2. Competitive inhibition Correct answer.
  3. Uncompetitive inhibition
  4. Non-competitive inhibition

Explanation

A competitive inhibitor binds reversibly at the active site, so increasing substrate concentration can outcompete it. The other types are not reversed simply by raising substrate concentration.

Question 5Sciences (Biology, Chemistry, Physics, related subjects)

Which factor best explains the decrease in atomic radius across Period 3 from sodium to chlorine?

  1. More electron shells are added
  2. Outer-shell electrons are removed
  3. Greater effective nuclear charge Correct answer.
  4. Increased shielding outweighs nuclear charge

Explanation

Across Period 3 the number of protons increases while electrons enter the same shell, so shielding is roughly constant. The resulting greater effective nuclear charge pulls the outer electrons closer.

Question 6Sciences (Biology, Chemistry, Physics, related subjects)

A 6.0 Ω resistor and a 3.0 Ω resistor are connected in series across an ideal 12 V battery. What current flows through the 6.0 Ω resistor?

  1. 1.5 A
  2. 1.3 A Correct answer.
  3. 0.75 A
  4. 4.0 A

Explanation

In a series circuit the same current passes through both resistors. Total resistance is 6.0 + 3.0 = 9.0 Ω, so I = V/R = 12/9.0 ≈ 1.3 A.

Question 7Sciences (Biology, Chemistry, Physics, related subjects)

Two heterozygous pea plants (Tt) are crossed. Assuming complete dominance for this single gene, what proportion of offspring is expected to show the recessive phenotype?

  1. 3/4
  2. 0
  3. 1/2
  4. 1/4 Correct answer.

Explanation

A Tt × Tt cross gives genotype ratios 1 TT : 2 Tt : 1 tt. Only tt shows the recessive phenotype, so the expected proportion is 1/4.

Question 8Sciences (Biology, Chemistry, Physics, related subjects)

Methane burns in oxygen: CH4(g) + 2O2(g) → CO2(g) + 2H2O(g). If 8.0 g CH4 (M = 16 g/mol) reacts with 24.0 g O2 (M = 32 g/mol), what is the limiting reactant and the amount of CO2 produced?

  1. O2 is limiting; 0.75 mol CO2 is produced.
  2. CH4 is limiting; 0.50 mol CO2 is produced.
  3. O2 is limiting; 0.375 mol CO2 is produced. Correct answer.
  4. CH4 is limiting; 0.25 mol CO2 is produced.

Explanation

n(CH4) = 8.0/16 = 0.50 mol and n(O2) = 24.0/32 = 0.75 mol. The methane would need 1.00 mol O2, so O2 is limiting; CO2 formed = 0.75/2 = 0.375 mol.

Question 9Sciences (Biology, Chemistry, Physics, related subjects)

A ray of light in glass of refractive index 1.50 strikes a glass-air boundary. What is the critical angle?

  1. 90.0°
  2. 48.2°
  3. 30.0°
  4. 41.8° Correct answer.

Explanation

At the critical angle the refracted ray travels along the boundary, so Snell's law gives sin c = n2/n1 = 1.00/1.50. Thus c = sin⁻¹(0.667) ≈ 41.8°.

Question 10Sciences (Biology, Chemistry, Physics, related subjects)

In the light-dependent reactions of photosynthesis, what is the main role of NADP+?

  1. It phosphorylates ADP to form ATP
  2. It fixes carbon dioxide into glucose
  3. It is reduced to NADPH Correct answer.
  4. It splits water to release oxygen

Explanation

NADP+ is the final electron acceptor of the light-dependent reactions and is reduced to NADPH. NADPH then carries reducing power to the Calvin cycle.

Question 11Sciences (Biology, Chemistry, Physics, related subjects)

A eukaryotic cell has an extensive network of rough endoplasmic reticulum. Which function is most directly associated with this organelle?

  1. DNA replication in the nucleus
  2. Protein synthesis for secretion Correct answer.
  3. ATP production by mitochondria
  4. Lipid synthesis for membranes

Explanation

Rough endoplasmic reticulum is studded with ribosomes, so it is the main site for synthesising proteins that will be secreted or inserted into membranes. Smooth endoplasmic reticulum, by contrast, is associated with lipid synthesis. Mitochondria produce most ATP, and DNA replication occurs in the nucleus.

Question 12Sciences (Biology, Chemistry, Physics, related subjects)

Which property increases down Group 1 of the periodic table?

  1. Electronegativity
  2. First ionisation energy
  3. Melting point of the metal
  4. Reactivity with water Correct answer.

Explanation

Down Group 1 the atoms become larger and the outer electron is farther from the nucleus and more shielded, so it is lost more readily. This makes the alkali metals more reactive with water. First ionisation energy, electronegativity and melting point generally decrease down the group.

Question 13Sciences (Biology, Chemistry, Physics, related subjects)

A student walks 3 m east and then 4 m north. Which quantity describing the student's motion is a vector?

  1. Speed
  2. Mass
  3. Energy
  4. Displacement Correct answer.

Explanation

A vector has both magnitude and direction. Displacement specifies how far and in which direction an object has moved from its starting point. Mass, speed and energy are scalars because they have magnitude only.

Question 14Sciences (Biology, Chemistry, Physics, related subjects)

In humans, red-green colour blindness is caused by a recessive allele on the X chromosome. A carrier woman and a man with normal colour vision have a son. What is the probability that the son is colour blind?

  1. 50% Correct answer.
  2. 0%
  3. 75%
  4. 25%

Explanation

The mother is a carrier, so she has one normal allele and one recessive colour-blindness allele on her X chromosomes. The father has normal colour vision and passes his Y chromosome to a son, so the son's X chromosome comes from the mother. Half of the mother's X-bearing gametes carry the recessive allele, giving a 50% probability that the son is colour blind.

Question 15Sciences (Biology, Chemistry, Physics, related subjects)

A 25.0 mL sample of 0.100 mol L−1 HCl is diluted with water to a final volume of 250.0 mL. What is the pH of the diluted solution?

  1. 1.00
  2. 2.00 Correct answer.
  3. 12.00
  4. 3.00

Explanation

Diluting 25.0 mL to 250.0 mL decreases the concentration by a factor of ten, so the hydrogen ion concentration falls from 0.100 mol L−1 to 0.0100 mol L−1. HCl is a strong monoprotic acid, so pH = −log10(0.0100) = 2.00.

Question 16Sciences (Biology, Chemistry, Physics, related subjects)

A wave source vibrates at 250 Hz and sends a wave along a string at 125 m/s. What is the distance between consecutive crests of the wave?

  1. 0.20 m
  2. 31 250 m
  3. 2.0 m
  4. 0.50 m Correct answer.

Explanation

The distance between consecutive crests is one wavelength. Using the wave equation v = fλ gives λ = v/f = 125 m s−1 ÷ 250 Hz = 0.50 m.

Question 17Sciences (Biology, Chemistry, Physics, related subjects)

In a food chain, only about 10% of the energy available at one trophic level is transferred to the next. Which statement best explains this low efficiency?

  1. Energy is destroyed when organisms are eaten.
  2. Consumers digest all the energy contained in their food.
  3. Much energy is lost as heat through respiration and in undigested material. Correct answer.
  4. Most energy is converted to biomass by the consumers.

Explanation

At each trophic level organisms use energy for respiration, and much of it is released as heat; some material is also not digested or is lost in waste. Only the energy incorporated into new biomass is available to the next trophic level. Energy is not destroyed, but it is transferred to the environment and becomes less useful.

Question 18Sciences (Biology, Chemistry, Physics, related subjects)

For the exothermic reaction N2(g) + 3H2(g) ⇌ 2NH3(g), which change would increase the equilibrium yield of ammonia?

  1. Increasing the temperature
  2. Adding a catalyst
  3. Removing nitrogen gas
  4. Increasing the pressure by decreasing the volume Correct answer.

Explanation

The forward reaction produces fewer gas moles, changing from 4 mol of gas reactants to 2 mol of gas product. Increasing pressure therefore shifts the equilibrium to the right and increases the yield of ammonia. Because the forward reaction is exothermic, increasing temperature shifts equilibrium left, and a catalyst does not change the equilibrium position.

Question 19Sciences (Biology, Chemistry, Physics, related subjects)

A satellite moves in a circular orbit of radius r around Earth with period T. If it is moved to a circular orbit of radius 4r, what is its new orbital period?

  1. 8T Correct answer.
  2. 4T
  3. 16T
  4. 2T

Explanation

Kepler's third law states that T² is proportional to r³ for orbits around the same central body. If the radius increases by a factor of 4, then T² increases by 4³ = 64, so T increases by a factor of 8. The new period is therefore 8T.

Question 20Sciences (Biology, Chemistry, Physics, related subjects)

When core body temperature rises above the set point, which response is produced by negative feedback?

  1. Sweating increases and skin blood vessels dilate. Correct answer.
  2. Metabolic rate increases to generate more heat.
  3. Muscles contract rapidly to produce heat.
  4. Shivering begins and blood vessels constrict.

Explanation

Negative feedback opposes the change. When core temperature rises, thermoreceptors detect the increase and the hypothalamus triggers responses that promote heat loss, such as sweating and dilation of skin blood vessels. Shivering, vasoconstriction and increased heat production are responses to cooling.

Question 21Sciences (Biology, Chemistry, Physics, related subjects)

In the fluid mosaic model of the plasma membrane, which component helps maintain membrane fluidity by preventing phospholipid tails from packing too tightly at low temperatures?

  1. Cholesterol Correct answer.
  2. Glycolipids
  3. Peripheral membrane proteins
  4. Integral membrane proteins

Explanation

Cholesterol is a steroid molecule embedded between phospholipid tails in the membrane. At low temperatures it disrupts ordered packing and helps keep the membrane fluid, while at high temperatures it reduces excessive fluidity. Proteins and glycolipids contribute mainly to transport, signalling, and recognition rather than this temperature-buffering role.

Question 22Sciences (Biology, Chemistry, Physics, related subjects)

Which type of bonding holds the ions together in a solid crystal of sodium chloride?

  1. Hydrogen bonding
  2. Metallic bonding
  3. Covalent bonding
  4. Ionic bonding Correct answer.

Explanation

Sodium chloride is made of Na+ and Cl− ions arranged in a giant ionic lattice. The strong electrostatic attraction between oppositely charged ions is ionic bonding. Metallic bonding occurs in metals, covalent bonding involves shared electron pairs, and hydrogen bonding is a weaker intermolecular attraction.

Question 23Sciences (Biology, Chemistry, Physics, related subjects)

A book rests on a horizontal table. The gravitational force of Earth on the book is one force in an action–reaction pair. Which force is its Newton's third law partner?

  1. The normal force of the table on the book
  2. The gravitational force of the book on Earth Correct answer.
  3. The frictional force of the table on the book
  4. The weight of the table

Explanation

Newton's third law pairs are equal in magnitude, opposite in direction, act on different objects, and are the same type of force. Earth pulls the book downward, so the partner force is the book pulling Earth upward. The normal force is not the partner because it is a contact force acting on the book, while the book's weight is a gravitational force acting on the book.

Question 24Sciences (Biology, Chemistry, Physics, related subjects)

During DNA replication, which enzyme joins Okazaki fragments on the lagging strand by forming phosphodiester bonds between adjacent nucleotides?

  1. DNA ligase Correct answer.
  2. DNA helicase
  3. RNA primase
  4. DNA polymerase

Explanation

DNA ligase seals the nicks between Okazaki fragments, forming the final phosphodiester bonds that join the sugar-phosphate backbone. DNA helicase unwinds the double helix, DNA polymerase synthesises new strands, and RNA primase makes the primers needed to start synthesis.

Question 25Sciences (Biology, Chemistry, Physics, related subjects)

A fixed mass of an ideal gas occupies 200 cm³ at 300 K and 100 kPa. What volume will it occupy at 400 K and 200 kPa?

  1. 75 cm³
  2. 300 cm³
  3. 267 cm³
  4. 133 cm³ Correct answer.

Explanation

Use the combined gas law: V2 = V1 × (P1/P2) × (T2/T1). Substituting gives 200 × (100/200) × (400/300) = 133 cm³. Temperatures must be expressed in kelvin, and the pressure and volume units must be consistent.

Question 26Sciences (Biology, Chemistry, Physics, related subjects)

A proton moving horizontally to the right enters a uniform magnetic field directed into the page. At the instant it enters the field, in which direction is the magnetic force on the proton?

  1. Into the page
  2. Upward, toward the top of the page Correct answer.
  3. Downward, toward the bottom of the page
  4. Out of the page

Explanation

For a positive charge, the magnetic force is given by F = qv × B. Using the right-hand rule, velocity to the right and magnetic field into the page give a force upward on the page. The force is perpendicular to both velocity and field, so it is not directed into or out of the page.

Question 27Sciences (Biology, Chemistry, Physics, related subjects)

An insect population is exposed to an insecticide for many generations. A few individuals carry a mutation that gives resistance, and the proportion of resistant insects rises. Which process best explains this increase?

  1. Natural selection favours resistant individuals, which survive and reproduce. Correct answer.
  2. Resistant insects learn to avoid the insecticide and pass the trait to offspring.
  3. Genetic drift randomly increases the resistance allele in every generation.
  4. The insecticide causes resistant mutations in individual insects.

Explanation

The resistance mutation already exists in some individuals, and the insecticide acts as a selective pressure. Resistant insects survive and reproduce more successfully, so the resistance allele increases in frequency over generations. Mutations are not directed by the insecticide, and learned avoidance is not inherited.

Question 28Sciences (Biology, Chemistry, Physics, related subjects)

Which pure substance has the highest boiling point?

  1. Ammonia, NH₃
  2. Methane, CH₄
  3. Water, H₂O Correct answer.
  4. Hydrogen chloride, HCl

Explanation

Water molecules form extensive hydrogen bonds, with each molecule able to donate and accept hydrogen bonds, giving strong intermolecular attraction. Ammonia also hydrogen bonds but less extensively, while methane and hydrogen chloride have weaker dispersion or dipole–dipole forces. Therefore water has the highest boiling point among these substances.

Question 29Sciences (Biology, Chemistry, Physics, related subjects)

Light of wavelength 400 nm strikes a metal surface with a work function of 2.0 eV. What is the maximum kinetic energy of the emitted photoelectrons? (h = 6.63 × 10⁻³⁴ J s, c = 3.00 × 10⁸ m s⁻¹, 1 eV = 1.60 × 10⁻¹⁹ J)

  1. 5.1 eV
  2. 3.1 eV
  3. 1.1 eV Correct answer.
  4. 2.0 eV

Explanation

The photon energy is E = hc/λ = (6.63 × 10⁻³⁴ × 3.00 × 10⁸)/(400 × 10⁻⁹) = 4.97 × 10⁻¹⁹ J, which is about 3.1 eV. The maximum kinetic energy is the photon energy minus the work function: 3.1 eV − 2.0 eV = 1.1 eV.

Question 30Sciences (Biology, Chemistry, Physics, related subjects)

A single nucleotide is inserted near the start of a protein-coding gene. Which outcome is most likely?

  1. No amino acids change because the genetic code is degenerate.
  2. One amino acid is replaced, and the rest of the sequence is unchanged.
  3. The mRNA is not transcribed, so no protein is made.
  4. The reading frame shifts, so many downstream amino acids are altered. Correct answer.

Explanation

Inserting one nucleotide changes the grouping of bases into codons from that point onward, causing a frameshift. This usually alters many amino acids and often creates a premature stop codon, so the protein is likely to be nonfunctional. A single substitution, not an insertion, typically changes only one codon.

Question 31Sciences (Biology, Chemistry, Physics, related subjects)

A liver cell contains many lysosomes. Which primary function do these organelles perform?

  1. Digesting organelles using hydrolytic enzymes Correct answer.
  2. Translating mRNA into polypeptides
  3. Synthesising ATP by oxidative phosphorylation
  4. Packaging proteins for exocytosis

Explanation

Lysosomes contain hydrolytic enzymes that operate at acidic pH and fuse with damaged organelles or vesicles to digest their contents. They do not synthesise ATP, package proteins for exocytosis, or translate mRNA; those roles belong to mitochondria, the Golgi apparatus, and ribosomes respectively.

Question 32Sciences (Biology, Chemistry, Physics, related subjects)

Across Period 3 from sodium to chlorine, which trend is observed?

  1. Atomic radius decreases Correct answer.
  2. Metallic character increases
  3. First ionisation energy decreases
  4. Electronegativity decreases

Explanation

Across Period 3, the nuclear charge increases while electrons are added to the same shell, so the atomic radius decreases. Electronegativity and first ionisation energy increase, and metallic character decreases.

Question 33Sciences (Biology, Chemistry, Physics, related subjects)

A hockey puck slides at constant velocity across a horizontal frictionless ice surface. Neglecting air resistance, what is the net force acting on the puck?

  1. A constant forward force equal to its weight
  2. A forward force that balances air resistance
  3. Zero Correct answer.
  4. A downward force equal to its weight

Explanation

Constant velocity means the puck has zero acceleration, so Newton's second law requires the net force to be zero. The weight is balanced by the normal force, and on frictionless ice no horizontal force is needed to maintain motion.

Question 34Sciences (Biology, Chemistry, Physics, related subjects)

In a dihybrid cross between two individuals heterozygous for both genes (AaBb × AaBb), assuming independent assortment, what fraction of offspring is expected to show both recessive phenotypes?

  1. 9/16
  2. 1/16 Correct answer.
  3. 3/16
  4. 1/4

Explanation

For each gene, the probability that an offspring is homozygous recessive is 1/4. With independent assortment, the joint probability is (1/4) × (1/4) = 1/16.

Question 35Sciences (Biology, Chemistry, Physics, related subjects)

In the electrolysis of molten sodium chloride, which product is formed at the cathode?

  1. Sodium metal Correct answer.
  2. Chlorine gas
  3. Hydrogen gas
  4. Oxygen gas

Explanation

At the cathode, reduction occurs: Na+ ions gain electrons to form sodium metal. Chloride ions are oxidised at the anode to chlorine gas.

Question 36Sciences (Biology, Chemistry, Physics, related subjects)

Two resistors, 6 Ω and 3 Ω, are connected in parallel across a 12 V battery of negligible internal resistance. What is the total current drawn from the battery?

  1. 6 A Correct answer.
  2. 2 A
  3. 8 A
  4. 4 A

Explanation

In parallel, each resistor has the full 12 V across it, so the currents are 12/6 = 2 A and 12/3 = 4 A. The total current is 2 + 4 = 6 A, and the equivalent resistance is 2 Ω.

Question 37Sciences (Biology, Chemistry, Physics, related subjects)

Which process converts atmospheric nitrogen gas into a form usable by plants?

  1. Nitrification
  2. Ammonification
  3. Nitrogen fixation Correct answer.
  4. Denitrification

Explanation

Nitrogen fixation is the conversion of atmospheric N2 into ammonia or related compounds by nitrogen-fixing bacteria such as Rhizobium. Nitrification, denitrification, and ammonification transform nitrogen between other chemical forms.

Question 38Sciences (Biology, Chemistry, Physics, related subjects)

What mass of sodium chloride is required to prepare 250.0 mL of a 0.200 mol L−1 solution? (M NaCl = 58.44 g mol−1)

  1. 5.84 g
  2. 11.7 g
  3. 2.92 g Correct answer.
  4. 0.731 g

Explanation

The amount in moles is n = cV = 0.200 mol L−1 × 0.2500 L = 0.0500 mol. The mass is n × M = 0.0500 mol × 58.44 g mol−1 = 2.922 g, which rounds to 2.92 g.

Question 39Sciences (Biology, Chemistry, Physics, related subjects)

A 0.20 kg ball strikes a wall horizontally at 10 m/s and rebounds horizontally at 8 m/s. If the contact time is 0.010 s, what is the magnitude of the average force exerted by the wall on the ball?

  1. 200 N
  2. 360 N Correct answer.
  3. 40 N
  4. 400 N

Explanation

Taking the rebound direction as positive, the change in momentum is Δp = m(vf − vi) = 0.20(8 − (−10)) = 3.6 kg m s−1. The average force is F = Δp/Δt = 3.6/0.010 = 360 N.

Question 40Sciences (Biology, Chemistry, Physics, related subjects)

A buffer solution contains equal concentrations of ethanoic acid and sodium ethanoate. When a small amount of hydrochloric acid is added, which species reacts with the added H+ and what is the effect on pH?

  1. Ethanoate ion reacts, and the pH increases only slightly
  2. Ethanoic acid reacts, and the pH decreases only slightly
  3. Ethanoic acid reacts, and the pH increases only slightly
  4. Ethanoate ion reacts, and the pH decreases only slightly Correct answer.

Explanation

A buffer of ethanoic acid and ethanoate contains a weak acid and its conjugate base. Added H+ is neutralised by the ethanoate ion, forming more ethanoic acid, so the pH decreases only slightly rather than sharply.

Question 41Sciences (Biology, Chemistry, Physics, related subjects)

During translation in a eukaryotic cell, which molecule delivers the correct amino acid to the ribosome?

  1. Ribosomal RNA
  2. Messenger RNA
  3. DNA polymerase
  4. Transfer RNA Correct answer.

Explanation

Transfer RNA carries a specific amino acid and has an anticodon that base-pairs with the matching codon on mRNA. Messenger RNA carries the coding sequence, while ribosomal RNA forms part of the ribosome. DNA polymerase is involved in DNA replication, not in delivering amino acids.

Question 42Sciences (Biology, Chemistry, Physics, related subjects)

The reaction of ethene with hydrogen in the presence of a nickel catalyst produces ethane. This reaction is best classified as:

  1. substitution
  2. addition Correct answer.
  3. elimination
  4. oxidation

Explanation

The carbon–carbon double bond opens and hydrogen atoms add across it, so the reaction is an addition reaction. This specific addition of hydrogen is called hydrogenation. No atom or group is removed or replaced in the process.

Question 43Sciences (Biology, Chemistry, Physics, related subjects)

Which of the following quantities used to describe motion is a vector?

  1. Distance
  2. Time
  3. Displacement Correct answer.
  4. Speed

Explanation

A vector quantity has both magnitude and direction. Displacement specifies how far and in which direction an object has moved from its starting point. Distance, speed, and time have magnitude only and are scalars.

Question 44Sciences (Biology, Chemistry, Physics, related subjects)

A population is in Hardy–Weinberg equilibrium for a gene with two alleles. If the frequency of the recessive allele is 0.30, what proportion of the population is expected to be heterozygous?

  1. 0.70
  2. 0.21
  3. 0.49
  4. 0.42 Correct answer.

Explanation

If q = 0.30, then p = 1 − 0.30 = 0.70. The expected heterozygous frequency is 2pq = 2 × 0.70 × 0.30 = 0.42. This follows from the Hardy–Weinberg expansion p² + 2pq + q² = 1.

Question 45Sciences (Biology, Chemistry, Physics, related subjects)

For the exothermic equilibrium reaction N2(g) + 3H2(g) ⇌ 2NH3(g), which change will shift the position of equilibrium toward the products?

  1. Removing ammonia as it forms Correct answer.
  2. Decreasing the total gas pressure
  3. Increasing the reaction temperature
  4. Adding a catalyst to the reaction mixture

Explanation

Removing ammonia lowers the product concentration, so the equilibrium shifts to the right to replace some of the removed ammonia. For this exothermic forward reaction, increasing temperature shifts the equilibrium to the left. Decreasing pressure shifts it toward the side with more gas molecules, which is the reactant side.

Question 46Sciences (Biology, Chemistry, Physics, related subjects)

A 0.50 kg cart moving at 4.0 m s−1 collides with a stationary 1.5 kg cart. The two carts stick together. What is their common speed immediately after the collision?

  1. 1.3 m s−1
  2. 0.50 m s−1
  3. 1.0 m s−1 Correct answer.
  4. 2.0 m s−1

Explanation

Total momentum before the collision is 0.50 kg × 4.0 m s−1 = 2.0 kg m s−1. After the collision the combined mass is 2.0 kg, so momentum conservation gives v = 2.0 kg m s−1 ÷ 2.0 kg = 1.0 m s−1. The collision is perfectly inelastic because the carts stick together.

Question 47Sciences (Biology, Chemistry, Physics, related subjects)

In recombinant DNA technology, what is the main role of a restriction enzyme?

  1. It joins DNA fragments by forming phosphodiester bonds.
  2. It amplifies a target DNA sequence through repeated cycles.
  3. It synthesises cDNA from an mRNA template.
  4. It cuts DNA at specific recognition sequences. Correct answer.

Explanation

Restriction endonucleases recognise specific base sequences and cleave the sugar–phosphate backbone at or near those sites. This produces DNA fragments with sticky or blunt ends that can be joined to other DNA. Ligase joins fragments, reverse transcriptase makes cDNA, and PCR amplifies DNA.

Question 48Sciences (Biology, Chemistry, Physics, related subjects)

In a galvanic cell operating spontaneously, at which electrode does oxidation occur and what is the sign of that electrode?

  1. Cathode, negative
  2. Cathode, positive
  3. Anode, positive
  4. Anode, negative Correct answer.

Explanation

Oxidation is the loss of electrons and occurs at the anode. In a galvanic cell the anode is the negative electrode, from which electrons flow through the external circuit toward the cathode. Reduction occurs at the positive cathode.

Question 49Sciences (Biology, Chemistry, Physics, related subjects)

A particle of mass m and charge q is accelerated from rest through a potential difference V. It then enters a uniform magnetic field of magnitude B perpendicular to its velocity. Which expression gives the radius of its circular path?

  1. sqrt(2mV/q)/B Correct answer.
  2. sqrt(2mVq)/B
  3. m sqrt(2qV)/(qB)
  4. sqrt(2qV/m)/B

Explanation

The accelerating voltage gives qV = ½mv², so the speed is v = sqrt(2qV/m). The magnetic force provides centripetal force, qvB = mv²/r, so r = mv/(qB). Substituting the speed gives r = sqrt(2mV/q)/B.

Question 50Sciences (Biology, Chemistry, Physics, related subjects)

Why is the second ionisation energy of sodium much greater than its first ionisation energy?

  1. The next electron is removed from a full inner shell closer to the nucleus. Correct answer.
  2. Sodium has a stable half-filled 3p subshell after the first electron is removed.
  3. The second electron is removed from the 3p subshell, which is higher in energy than the 3s subshell.
  4. The first electron is removed from an inner shell, while the second is removed from the valence shell.

Explanation

Sodium’s first ionisation removes its single 3s valence electron, leaving Na+ with the stable neon configuration. The second ionisation must therefore remove an electron from the n = 2 shell, which is closer to the nucleus and experiences a much greater effective nuclear charge. This requires substantially more energy.