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AP SSC General Science (BSEAP) study materials
AP SSC General Science (BSEAP) study resources

AP SSC General Science (BSEAP) practice questions

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Question 1Reflection of Light at Curved Surfaces

A concave mirror is described as a converging mirror. Which statement explains why parallel rays of light incident on it are brought together?

  1. The reflecting surface curves outward, so normals at different points tilt the rays away from the principal axis
  2. The pole of the mirror reflects every ray back along its own path
  3. The reflecting surface curves inward, so normals at different points tilt the rays toward the principal axis Correct answer.
  4. The mirror refracts the rays as they pass through the silvered layer

Explanation

In a concave mirror the silvered surface bulges away from the incident light, so the reflecting face is a hollow bowl. The normal at each point is a radius of the sphere, and rays parallel to the principal axis strike at different angles and are turned inward, meeting near the focus.

Question 2Reflection of Light at Curved Surfaces

For a spherical mirror of radius of curvature 30 cm, what is the focal length, and where does the focus lie relative to the pole?

  1. 7.5 cm, midway between the focus and the centre of curvature
  2. 30 cm, at the centre of curvature itself
  3. 60 cm, measured from the centre of curvature
  4. 15 cm, midway between the pole and the centre of curvature Correct answer.

Explanation

For a spherical mirror the focal length is half the radius of curvature, f = R/2. With R = 30 cm, f = 15 cm, and the focus lies on the principal axis halfway between the pole and the centre of curvature.

Question 3Reflection of Light at Curved Surfaces

A ray of light travelling parallel to the principal axis strikes a convex mirror. After reflection, how does the ray behave?

  1. It appears to diverge from the virtual focus behind the mirror Correct answer.
  2. It reflects back along its original path
  3. It passes undeviated straight through the mirror
  4. It passes through the focus on the same side as the incident light

Explanation

A convex mirror diverges parallel rays. The reflected rays spread out, and when produced backwards they appear to come from a point behind the mirror, the virtual principal focus.

Question 4Reflection of Light at Curved Surfaces

An object is placed at the centre of curvature of a concave mirror. Which description of the image is correct?

  1. Real, inverted and of the same size as the object Correct answer.
  2. Virtual, inverted and diminished
  3. Virtual, erect and enlarged
  4. Real, inverted and diminished

Explanation

When the object stands at the centre of curvature, the image forms at the centre of curvature on the same side. It is real, inverted and exactly the same size as the object, with magnification of magnitude one.

Question 5Reflection of Light at Curved Surfaces

An object 4 cm tall is placed 30 cm in front of a concave mirror of focal length 10 cm. Using the mirror formula, what is the image distance and the nature of the image?

  1. 15 cm in front of the mirror, real Correct answer.
  2. 15 cm behind the mirror, virtual
  3. 20 cm in front of the mirror, real
  4. 7.5 cm in front of the mirror, real

Explanation

With u = -30 cm and f = -10 cm, the mirror formula 1/v + 1/u = 1/f gives 1/v = -1/10 + 1/30 = -1/15, so v = -15 cm. The negative sign places the image 15 cm in front of the mirror, so it is real.

Question 6Reflection of Light at Curved Surfaces

An object is placed 12 cm in front of a convex mirror whose focal length is 6 cm. Where is the image formed?

  1. 6 cm in front of the mirror
  2. 4 cm in front of the mirror
  3. 12 cm behind the mirror
  4. 4 cm behind the mirror Correct answer.

Explanation

For a convex mirror, f is taken as positive and u as negative. Using 1/v + 1/u = 1/f with u = -12 cm and f = +6 cm gives 1/v = 1/6 + 1/12 = 1/4, so v = +4 cm. The positive value means the image lies 4 cm behind the mirror and is virtual.

Question 7Reflection of Light at Curved Surfaces

A concave mirror forms a real image that is three times the height of the object. If the object is 20 cm from the pole, what is the image distance from the pole?

  1. 60 cm, on the same side as the object Correct answer.
  2. 20 cm, on the same side as the object
  3. 60 cm, on the opposite side from the object
  4. 6.7 cm, on the same side as the object

Explanation

Magnification m = -v/u, so a real image three times as tall with u = -20 cm gives v = -60 cm. The negative sign indicates the image is real and lies 60 cm in front of the mirror, on the same side as the object.

Question 8Reflection of Light at Curved Surfaces

Why is a convex mirror preferred as a rear-view mirror in vehicles?

  1. It forms a magnified real image of distant traffic
  2. It absorbs stray light and prevents glare completely
  3. It gives an erect, diminished image and therefore a wider field of view Correct answer.
  4. It always forms an image at the centre of curvature

Explanation

A convex mirror always produces a virtual, erect and diminished image for a real object. Because the image is smaller, more of the scene fits into the mirror, giving the driver a wider field of view behind the vehicle.

Question 9Reflection of Light at Curved Surfaces

A dentist uses a small concave mirror to examine a tooth. To obtain an erect, enlarged image, where must the tooth be placed?

  1. Between the pole and the principal focus Correct answer.
  2. Beyond the centre of curvature of the mirror
  3. At a distance equal to twice the focal length
  4. Exactly at the centre of curvature

Explanation

For a concave mirror, an object placed between the pole and the focus gives a virtual, erect and magnified image. That is the arrangement a dentist needs so the tooth appears larger and upright.

Question 10Reflection of Light at Curved Surfaces

An object is moved from a point far beyond the centre of curvature of a concave mirror toward the principal focus. How do the size and position of the real image change?

  1. The image moves toward the centre of curvature and stays the same size
  2. The image becomes virtual as soon as the object passes the centre of curvature
  3. The image moves away from the mirror and becomes larger Correct answer.
  4. The image moves toward the focus and becomes smaller

Explanation

As the object moves from infinity toward the focus, the real image moves from the focus outward beyond the centre of curvature. Its magnification increases, so the image grows larger as it recedes from the mirror.

Question 11Reflection of Light at Curved Surfaces

A ray of light directed toward the centre of curvature of a concave mirror strikes the mirror. What happens to it after reflection?

  1. It is reflected parallel to the principal axis
  2. It retraces its path back along the same line Correct answer.
  3. It is reflected through the principal focus
  4. It is reflected at an angle equal to the angle of incidence but away from the axis

Explanation

A ray aimed at the centre of curvature travels along a radius of the sphere, so it meets the surface normally, with zero angle of incidence. It is therefore reflected straight back along its own path.

Question 12Reflection of Light at Curved Surfaces

A concave mirror of focal length 10 cm is used to form a real image that is exactly twice the size of the object. Which pair of object and image distances satisfies this condition?

  1. u = 30 cm, v = 15 cm
  2. u = 15 cm, v = 30 cm Correct answer.
  3. u = 10 cm, v = 20 cm
  4. u = 20 cm, v = 40 cm

Explanation

A real image twice the object size needs magnification of magnitude 2, so v = 2u. Substituting into 1/v + 1/u = 1/f with f = 10 cm gives 3/(2u) = 1/10, hence u = 15 cm and v = 30 cm.

Question 13Chemical Reactions and Equations

In the reaction Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g), which substance is oxidised and what is its change in oxidation state?

  1. Chlorine, from -1 to 0
  2. Zinc, from +2 to 0
  3. Zinc, from 0 to +2 Correct answer.
  4. Hydrogen, from +1 to 0

Explanation

Oxidation is a loss of electrons, shown by an increase in oxidation state. Zinc starts as a free element with oxidation state 0 and ends as Zn²⁺ in ZnCl₂, so it is oxidised. Hydrogen is reduced from +1 to 0, and chlorine stays at -1 throughout.

Question 14Chemical Reactions and Equations

Which of the following is the correctly balanced equation for the reaction of aluminium with dilute hydrochloric acid?

  1. Al + HCl → AlCl₃ + H₂
  2. 2Al + 3HCl → AlCl₃ + H₂
  3. Al + 3HCl → AlCl₃ + 3H₂
  4. 2Al + 6HCl → 2AlCl₃ + 3H₂ Correct answer.

Explanation

A balanced equation must have equal numbers of each kind of atom on both sides. Using 2Al + 6HCl gives 2 Al, 6 Cl and 6 H on the left, and 2AlCl₃ + 3H₂ also gives 2 Al, 6 Cl and 6 H on the right. Only this set of coefficients satisfies conservation of atoms.

Question 15Chemical Reactions and Equations

A student adds dilute sulphuric acid to sodium carbonate solution and observes brisk effervescence. The gas produced turns limewater milky. Which gas is evolved and what type of reaction is this?

  1. Carbon dioxide; neutralisation of a carbonate by an acid Correct answer.
  2. Sulphur dioxide; redox reaction
  3. Oxygen gas; decomposition reaction
  4. Hydrogen gas; displacement reaction

Explanation

Acids react with metal carbonates to release carbon dioxide, which turns limewater milky by forming insoluble calcium carbonate. The overall change, Na₂CO₃ + H₂SO₄ → Na₂SO₄ + H₂O + CO₂, is an acid–carbonate neutralisation producing a salt, water and carbon dioxide.

Question 16Chemical Reactions and Equations

In the reaction CuO + H₂ → Cu + H₂O carried out on heating, which statement correctly describes the roles of the reactants?

  1. Neither reactant changes oxidation state
  2. CuO is reduced and H₂ is oxidised Correct answer.
  3. CuO is oxidised and H₂ is reduced
  4. Both CuO and H₂ are oxidised

Explanation

Copper(II) oxide loses oxygen, so it is reduced to copper metal, while hydrogen gains oxygen and is oxidised to water. In terms of electrons, Cu²⁺ gains electrons and each H atom loses one electron. This is a classic reduction of a metal oxide by hydrogen.

Question 17Chemical Reactions and Equations

Which of the following equations represents a decomposition reaction?

  1. Zn + CuSO₄ → ZnSO₄ + Cu
  2. NaOH + HCl → NaCl + H₂O
  3. CaCO₃ → CaO + CO₂ on strong heating Correct answer.
  4. Fe + S → FeS on heating

Explanation

A decomposition reaction is one in which a single compound breaks down into two or more simpler substances, usually with heat, light or electricity. Calcium carbonate splitting into calcium oxide and carbon dioxide on strong heating fits this definition exactly.

Question 18Chemical Reactions and Equations

When an iron nail is kept in copper sulphate solution for some time, the blue colour fades and a reddish-brown deposit forms on the nail. What is the balanced equation and the type of reaction?

  1. Fe + CuSO₄ → Fe₂(SO₄)₃ + Cu; displacement
  2. Fe + CuSO₄ → FeSO₄ + Cu; displacement Correct answer.
  3. Cu + FeSO₄ → CuSO₄ + Fe; displacement
  4. Fe + CuSO₄ → FeS + CuO; decomposition

Explanation

Iron is more reactive than copper, so it displaces copper from copper(II) sulphate, giving iron(II) sulphate and copper metal. The equation Fe + CuSO₄ → FeSO₄ + Cu is already balanced and matches the observed fading of blue colour and brown deposit.

Question 19Chemical Reactions and Equations

Which pair of solutions, when mixed, produces a white precipitate of a double displacement reaction?

  1. Barium chloride and sodium sulphate Correct answer.
  2. Copper sulphate and iron filings
  3. Sodium hydroxide and hydrochloric acid
  4. Sodium chloride and potassium nitrate

Explanation

In a double displacement reaction the ions of two compounds exchange partners. Barium chloride with sodium sulphate gives barium sulphate, which is insoluble and appears as a white precipitate, along with sodium chloride in solution.

Question 20Chemical Reactions and Equations

A colourless gas is produced when zinc granules are added to dilute sulphuric acid. Which test and observation confirm the gas?

  1. It turns moist red litmus paper blue
  2. It burns with a pop sound when a burning splint is brought near Correct answer.
  3. It relights a glowing splint
  4. It turns limewater milky

Explanation

Zinc reacts with dilute sulphuric acid to give hydrogen gas, Zn + H₂SO₄ → ZnSO₄ + H₂. Hydrogen is combustible and burns with a characteristic pop sound when a burning splint is brought to the mouth of the test tube.

Question 21Chemical Reactions and Equations

In the reaction 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂ on heating, what is the colour of the gas NO₂ and what type of reaction occurs?

  1. Colourless gas; combination reaction
  2. Brown gas; thermal decomposition Correct answer.
  3. Greenish-yellow gas; displacement reaction
  4. White fumes; double displacement

Explanation

Lead(II) nitrate decomposes on heating into lead(II) oxide, nitrogen dioxide and oxygen. Nitrogen dioxide is a reddish-brown gas, and the breakdown of one compound into three products by heat is a thermal decomposition.

Question 22Chemical Reactions and Equations

Which observation shows that a chemical reaction has taken place when dilute hydrochloric acid is added to sodium hydroxide solution containing phenolphthalein?

  1. The solution becomes more strongly pink
  2. A gas is evolved briskly
  3. The pink colour of the solution disappears Correct answer.
  4. The temperature falls sharply

Explanation

Phenolphthalein is pink in alkaline solution and colourless in acidic or neutral solution. As hydrochloric acid neutralises the sodium hydroxide, the solution becomes neutral and the pink colour disappears, indicating a chemical change.

Question 23Chemical Reactions and Equations

In the reaction 2FeCl₂ + Cl₂ → 2FeCl₃, which species acts as the oxidising agent and why?

  1. Cl₂, because it gains electrons from iron(II) ions Correct answer.
  2. FeCl₂, because iron loses electrons
  3. Cl₂, because its oxidation state increases from 0 to -1
  4. FeCl₂, because it gains chlorine atoms

Explanation

An oxidising agent is the substance that gains electrons and is itself reduced. Here chlorine goes from oxidation state 0 to -1, gaining electrons, while iron(II) is oxidised to iron(III). Therefore chlorine is the oxidising agent.

Question 24Chemical Reactions and Equations

A balanced chemical equation is required for the combustion of ethanol, C₂H₅OH. Which equation is correctly balanced?

  1. C₂H₅OH + 2O₂ → 2CO₂ + 3H₂O
  2. C₂H₅OH + O₂ → CO₂ + H₂O
  3. C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O Correct answer.
  4. C₂H₅OH + 3O₂ → CO₂ + 3H₂O

Explanation

Ethanol contains 2 C, 6 H and 1 O. With 3O₂ on the left there are 2 C, 6 H and 7 O atoms, and 2CO₂ + 3H₂O on the right also gives 2 C, 6 H and 7 O atoms. Hence this is the correctly balanced combustion equation.

Question 25Chemical Reactions and Equations

A silvery-white metal burns in air with a dazzling white flame to give a white powder that dissolves in water to form an alkaline solution. Identify the metal and the product.

  1. Copper, giving copper(II) oxide
  2. Sodium, giving sodium oxide
  3. Magnesium, giving magnesium oxide Correct answer.
  4. Iron, giving iron(III) oxide

Explanation

Magnesium ribbon burns in air with a brilliant white flame forming magnesium oxide, a white powder. Magnesium oxide is basic and reacts with water to give magnesium hydroxide, which is alkaline to litmus.

Question 26Chemical Reactions and Equations

Which statement correctly distinguishes a displacement reaction from a double displacement reaction?

  1. Both types always produce a precipitate
  2. In displacement two compounds exchange ions, while in double displacement one element replaces another
  3. Displacement reactions always involve the evolution of a gas
  4. In displacement one element replaces another in a compound, while in double displacement two compounds exchange ions Correct answer.

Explanation

A displacement reaction involves a more reactive element taking the place of a less reactive element in its compound, as when zinc displaces copper from copper sulphate. A double displacement reaction involves the exchange of ions between two compounds in solution, often forming a precipitate.

Question 27Chemical Reactions and Equations

Consider the equation: MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂. Which element is oxidised and which is reduced in this reaction?

  1. Hydrogen is oxidised and oxygen is reduced
  2. Manganese is oxidised and chlorine is reduced
  3. Neither manganese nor chlorine changes oxidation state
  4. Chlorine is oxidised and manganese is reduced Correct answer.

Explanation

In MnO₂ manganese is +4 and in MnCl₂ it is +2, so manganese is reduced by gaining electrons. Part of the chlorine in HCl goes from -1 to 0 in Cl₂, which is oxidation, so chlorine is oxidised while manganese is reduced.

Question 28Chemical Reactions and Equations

Which of the following is an example of a photolytic decomposition reaction?

  1. 2KClO₃ → 2KCl + 3O₂ with MnO₂ catalyst
  2. CaCO₃ → CaO + CO₂ on heating
  3. 2AgCl → 2Ag + Cl₂ in sunlight Correct answer.
  4. Fe + CuSO₄ → FeSO₄ + Cu

Explanation

A photolytic decomposition is brought about by light. Silver chloride decomposes in sunlight into silver metal and chlorine gas, which is why it darkens and is used in photographic materials.

Question 29Acids, Bases and Salts

A solution turns blue litmus paper red. Which statement about the solution is correct?

  1. It is acidic and has a pH less than 7. Correct answer.
  2. It is neutral and has a pH equal to 7.
  3. It is basic and has a pH greater than 7.
  4. It is acidic and has a pH greater than 7.

Explanation

Litmus is red in acidic solutions and blue in basic solutions, so a colour change from blue to red shows the solution is acidic. Acidic solutions have a pH below 7 at room temperature. The two facts together identify the correct statement.

Question 30Acids, Bases and Salts

Which of the following is the correct formula of washing soda?

  1. NaCl
  2. NaHCO3
  3. Na2CO3·10H2O Correct answer.
  4. NaOH

Explanation

Washing soda is hydrated sodium carbonate, written as Na2CO3·10H2O, and it is a basic salt used in the laundry industry. The ten water molecules are part of its crystal structure. The other formulas belong to baking soda, common salt and caustic soda respectively.

Question 31Acids, Bases and Salts

Which ion is released in large amounts when an acid is dissolved in water?

  1. Sodium ion, Na+
  2. Hydrogen ion, H+ Correct answer.
  3. Hydroxide ion, OH-
  4. Chloride ion, Cl-

Explanation

An acid is a substance that gives hydrogen ions, H+, when dissolved in water; this is the Arrhenius definition used at this level. The H+ ions are what make the solution sour and turn blue litmus red. Hydroxide ions are characteristic of bases instead.

Question 32Acids, Bases and Salts

Which pair of substances will react to produce a salt and water only?

  1. Zinc and dilute sulphuric acid
  2. Sodium carbonate and dilute sulphuric acid
  3. Sodium hydroxide and dilute hydrochloric acid Correct answer.
  4. Copper and dilute hydrochloric acid

Explanation

The reaction between an acid and a base such as sodium hydroxide is neutralisation, and it produces only a salt and water. Metal-plus-acid reactions also release hydrogen gas, and carbonate-plus-acid reactions release carbon dioxide. Therefore only the acid-base pair fits the stated products.

Question 33Acids, Bases and Salts

A solution has a pH of 12. Which statement best describes it?

  1. It is strongly acidic and contains more H+ than OH- ions.
  2. It is strongly basic and contains more OH- than H+ ions. Correct answer.
  3. It is weakly acidic and contains more H+ than OH- ions.
  4. It is neutral because it contains equal H+ and OH- ions.

Explanation

A pH of 12 is well above 7, so the solution is strongly basic. In basic solutions the concentration of hydroxide ions exceeds that of hydrogen ions. This balance of ions is what produces the high pH value.

Question 34Acids, Bases and Salts

Which reaction explains why a farmer adds slaked lime to strongly acidic soil?

  1. The lime has no chemical effect and only loosens the soil.
  2. The lime neutralises excess acid in the soil and raises the pH. Correct answer.
  3. The lime converts the soil into a strongly basic mixture with pH 14.
  4. The lime adds more acid to the soil and lowers the pH.

Explanation

Slaked lime, calcium hydroxide, is a base, so it reacts with the excess acid in the soil in a neutralisation reaction. This raises the soil pH towards the range suitable for crops. Farmers use it because plants grow poorly in very acidic soil.

Question 35Acids, Bases and Salts

Which gas is produced when dilute hydrochloric acid is added to sodium carbonate?

  1. Carbon dioxide Correct answer.
  2. Oxygen
  3. Hydrogen
  4. Sulphur dioxide

Explanation

Acids react with carbonates to release carbon dioxide, which turns limewater milky. The other product is a salt, here sodium chloride, along with water. This test is the standard way to identify a carbonate.

Question 36Acids, Bases and Salts

What is the pH of a solution formed by mixing equal volumes of dilute hydrochloric acid and sodium hydroxide solution of the same concentration?

  1. About 14, because sodium hydroxide is a strong base.
  2. About 1, because the acid is stronger than the base.
  3. About 7, because the acid and base neutralise each other completely. Correct answer.
  4. About 4, because some acid always remains.

Explanation

When equal amounts of a strong acid and a strong base of the same concentration react, they neutralise each other exactly. The resulting solution contains only the neutral salt sodium chloride and water. Its pH is therefore close to 7.

Question 37Acids, Bases and Salts

Which property of dilute ethanoic acid shows that it is a weak acid?

  1. It turns blue litmus red.
  2. It reacts with sodium carbonate to give carbon dioxide.
  3. It conducts electricity very poorly and has a pH of about 3. Correct answer.
  4. It reacts with magnesium to give hydrogen.

Explanation

A weak acid is only partially ionised in water, so it gives a low concentration of H+ ions. This results in poor electrical conductivity and a pH that is only mildly acidic. Litmus colour and gas evolution are shown by strong acids as well, so they do not distinguish strength.

Question 38Acids, Bases and Salts

Which statement correctly describes the role of water in showing acidic behaviour?

  1. An acid produces H+ ions only in the presence of water. Correct answer.
  2. Water has no role; acids ionise in any liquid.
  3. An acid produces H+ ions only in the absence of water.
  4. Water reacts with an acid to form a base.

Explanation

Acids ionise to release hydrogen ions only when dissolved in water, because water molecules help separate the ions. Dry hydrogen chloride gas, for example, does not turn litmus red. This is why the definition of an acid refers to its behaviour in aqueous solution.

Question 39Acids, Bases and Salts

What is the correct chemical name of baking soda?

  1. Sodium carbonate
  2. Calcium carbonate
  3. Sodium chloride
  4. Sodium hydrogen carbonate Correct answer.

Explanation

Baking soda is sodium hydrogen carbonate, NaHCO3, a mild base used in cooking and as an antacid. It decomposes on heating to give sodium carbonate, carbon dioxide and water. Sodium carbonate is a different compound, washing soda.

Question 40Acids, Bases and Salts

A student adds a few drops of universal indicator to a solution and it turns green. What can be concluded?

  1. The solution is strongly acidic.
  2. The solution is weakly basic.
  3. The solution is neutral, with pH near 7. Correct answer.
  4. The solution is strongly basic.

Explanation

Universal indicator gives a green colour at pH values close to 7, which is the neutral range. Red and orange indicate acidity, while blue and violet indicate increasing basicity. Green therefore identifies a neutral solution.

Question 41Acids, Bases and Salts

Which salt is formed when dilute sulphuric acid reacts with magnesium hydroxide?

  1. Magnesium sulphate Correct answer.
  2. Magnesium carbonate
  3. Magnesium chloride
  4. Magnesium nitrate

Explanation

In a neutralisation reaction the metal of the base combines with the anion of the acid to form the salt. Sulphuric acid supplies sulphate ions, so the salt is magnesium sulphate. The other anions come from different acids.

Question 42Acids, Bases and Salts

Why does a solution of sodium chloride in water have a pH of about 7?

  1. It is formed from a strong acid and a strong base, so neither ion hydrolyses appreciably. Correct answer.
  2. It contains excess hydrochloric acid left over from its formation.
  3. It contains excess sodium hydroxide left over from its formation.
  4. Sodium chloride reacts with water to produce hydrogen ions.

Explanation

Sodium chloride is a salt of a strong acid, hydrochloric acid, and a strong base, sodium hydroxide. Neither Na+ nor Cl- reacts appreciably with water, so the solution stays neutral. This is why its pH is close to 7.

Question 43Acids, Bases and Salts

A student must prepare copper sulphate crystals from copper oxide. Which sequence of steps is correct?

  1. Add excess dilute sulphuric acid to copper oxide, filter, then crystallise the filtrate.
  2. Add excess copper oxide to warm dilute sulphuric acid, filter, then crystallise the filtrate. Correct answer.
  3. Heat copper oxide strongly, then dissolve the residue in water.
  4. Add copper oxide to water, stir, then evaporate to dryness.

Explanation

Copper oxide is a base and reacts with warm dilute sulphuric acid to form copper sulphate. Adding the oxide in excess ensures all the acid is used up, and the unreacted oxide is removed by filtration. The filtrate is then evaporated to crystallise the salt.

Question 44Acids, Bases and Salts

Dilute hydrochloric acid is added to four metals: copper, zinc, iron and silver. Which metals produce hydrogen gas?

  1. Zinc and iron only Correct answer.
  2. Copper and silver only
  3. Zinc, iron and copper
  4. All four metals

Explanation

A metal displaces hydrogen from a dilute acid only if it lies above hydrogen in the reactivity series. Zinc and iron are above hydrogen, so both react and release hydrogen. Copper and silver lie below hydrogen and do not react with dilute hydrochloric acid.

Question 45Refraction of Light at Plane Surfaces

A ray of light passes obliquely from air into a glass slab. Which statement correctly describes what happens to the ray at the air–glass boundary?

  1. It bends towards the normal because its speed decreases in glass Correct answer.
  2. It continues undeviated because glass is transparent
  3. It reflects back into air because glass has a higher refractive index
  4. It bends away from the normal because its speed increases in glass

Explanation

When light enters a denser medium from a rarer one, its speed falls and it bends towards the normal, in accordance with Snell's law. Since glass is optically denser than air, the refracted ray moves closer to the normal rather than away from it. Refraction, not total reflection, occurs at this boundary because the ray enters the second medium.

Question 46Refraction of Light at Plane Surfaces

The refractive index of a medium is defined as the ratio of the speed of light in vacuum to the speed of light in that medium. For a medium in which light travels at 2 × 10^8 m s^-1, what is its refractive index? (Speed of light in vacuum = 3 × 10^8 m s^-1)

  1. 0.67
  2. 1.5 Correct answer.
  3. 2.0
  4. 6.0

Explanation

Refractive index n equals the speed of light in vacuum divided by the speed in the medium, so n = (3 × 10^8)/(2 × 10^8) = 1.5. The value must be greater than one because light is slower in any material medium than in vacuum. This ratio is dimensionless, so no unit is attached.

Question 47Refraction of Light at Plane Surfaces

A ray of light strikes a plane glass surface at an angle of incidence of 40°. What is the angle between the refracted ray and the normal if the refractive index of the glass is 1.5? (sin 40° = 0.643)

  1. 30.0°
  2. 40.0°
  3. 50.0°
  4. 25.4° Correct answer.

Explanation

By Snell's law, n = sin i / sin r, so sin r = sin 40° / 1.5 = 0.643 / 1.5 = 0.429. The angle whose sine is 0.429 is about 25.4°, which is less than the angle of incidence, as expected when entering a denser medium. The refracted ray therefore lies closer to the normal than the incident ray.

Question 48Refraction of Light at Plane Surfaces

A fish looks upwards through still water (refractive index 4/3) towards the open air. What is the critical angle for the water–air boundary? (sin^-1 0.75 ≈ 48.6°)

  1. 53.1°
  2. 48.6° Correct answer.
  3. 90.0°
  4. 41.8°

Explanation

The critical angle satisfies sin C = 1/n for light going from the denser medium to air. With n = 4/3, sin C = 3/4 = 0.75, giving C ≈ 48.6°. Beyond this angle, rays striking the surface are totally internally reflected back into the water.

Question 49Refraction of Light at Plane Surfaces

A ray of light passes through a parallel-sided glass slab and emerges into air. Which statement about the emergent ray is correct?

  1. It is parallel to the incident ray but laterally displaced Correct answer.
  2. It converges towards the incident ray's line
  3. It emerges at a larger angle than the angle of incidence
  4. It emerges perpendicular to the incident ray

Explanation

At the first surface the ray bends towards the normal and at the second parallel surface it bends away by an equal amount, so the emergent ray is parallel to the incident ray. Because the two refractions occur at different points, the emergent ray is shifted sideways, producing lateral displacement. The displacement increases with slab thickness and angle of incidence.

Question 50Refraction of Light at Plane Surfaces

A coin lying at the bottom of a vessel of water appears raised when viewed from above. This apparent shift occurs because light from the coin

  1. bends towards the normal on leaving water, so the rays appear to come from a farther point
  2. travels faster in water than in air
  3. bends away from the normal on leaving water, so the rays appear to come from a nearer point Correct answer.
  4. is totally internally reflected at the water surface

Explanation

Light from the coin travels from water (denser) to air (rarer), so it bends away from the normal at the surface. To the observer, the backward-extended refracted rays meet at a point above the actual coin, making it appear raised. This is why a pool looks shallower than it really is.