CBSE Class 7 Science Advanced Chemistry Chemistry in Daily Life MCQs Set 04

Answer: (a) silver iodide

Explanation:
1. Fine particles of silver iodide act as nuclei on which water vapour condenses, so rain forms.
2. Copper sulphate and zinc sulphate are not used for this purpose.
3. The standard answer is silver iodide.

Teacher's Note:
1. Cloud seeding adds tiny particles for droplets to grow on.
2. Silver iodide crystals look like ice crystals.

Answer: (b) Lead pencils are made up of lead.

Explanation:
1. Tincture of iodine kills germs, graphite is used for electrodes, and iodine is a violet crystalline solid.
2. Pencil lead is not lead but graphite mixed with clay.
3. The incorrect statement is (b).

Teacher's Note:
1. Pencil 'lead' is a name from the past.
2. Graphite conducts electricity.

Answer: (d) Duralumin

Explanation:
1. Brass and bronze are mostly copper, and steel is mostly iron.
2. Duralumin is about 95% aluminium.
3. The answer is duralumin.

Teacher's Note:
1. Duralumin has 'alum' in its name.
2. It also contains small amounts of Cu, Mg and Mn.

Answer: (b) ADCB

Explanation:
1. Limestone \(\ce{CaCO3}\) has no water of crystallization (0).
2. Plaster of Paris CaSO₄·½H₂O has half a molecule (½).
3. Gypsum \(\ce{CaSO4.2H2O}\) has 2.
4. Blue vitriol \(\ce{CuSO4.5H2O}\) has 5.
5. The order is A, D, C, B: option (b).

Teacher's Note:
1. Count the H₂O written after the dot in each formula.
2. Plaster of Paris is gypsum that has lost most of its water.

Answer: (a) galvanization

Explanation:
1. Coating iron with zinc to prevent rusting is galvanization.
2. Tinning uses tin and amalgamation uses mercury.

Teacher's Note:
1. Galvanised iron (GI) sheets are zinc coated.
2. Zinc protects the iron even if the coating is scratched.

Answer: (d) (i) → (B); (ii) → (C); (iii) → (D); (iv) → (E)

Explanation:
1. Chlorine is used in making DDT: (i) → (B).
2. Iodine prevents and treats goitre: (ii) → (C).
3. Neon glows red and is used in advertising sign boards: (iii) → (D).
4. Radon is used in the treatment of cancer: (iv) → (E).
5. This is option (d).

Teacher's Note:
1. Neon signs are glass tubes that glow.
2. Radon is radioactive, so it is used for radiotherapy.

Answer: (b) Polyvinyl chloride

Explanation:
1. Bakelite and melamine are thermosetting, so they cannot be melted again and recycled.
2. Polyvinyl chloride (PVC) is a thermoplastic and can be recycled.
3. The answer is polyvinyl chloride.

Teacher's Note:
1. Recyclable means it can be re-melted: thermoplastic.
2. Both (a) and (c) names two thermosets.

Answer: (d) Potassium sulphate

Explanation:
1. The first three contain nitrogen and (in the first) phosphorus, but no potassium.
2. Potassium sulphate contains potassium.
3. The answer is potassium sulphate.

Teacher's Note:
1. Look for the word potassium in the name.
2. It is a potash fertilizer.

Answer: (b) Sodium silicate

Explanation:
1. Sodium silicate (water glass) dissolves in water, and eggs kept in its solution stay fresh because it seals the pores of the shell.
2. Silicon dioxide and silicon carbide are insoluble.
3. The answer is sodium silicate.

Teacher's Note:
1. Water glass is the common name of sodium silicate.
2. Sand, SiO₂, does not dissolve in water.

Answer: (c) BACD

Explanation:
1. Zinc oxide \(\ce{ZnO}\) has 1 oxygen atom.
2. Carbon dioxide \(\ce{CO2}\) has 2.
3. Calcium carbonate \(\ce{CaCO3}\) has 3.
4. Calcium sulphate \(\ce{CaSO4}\) has 4.
5. The order is B, A, C, D: option (c).

Teacher's Note:
1. Write each formula and count the O atoms.
2. Sulphate has 4 oxygens and carbonate has 3.

Answer: (c) protein

Explanation:
1. Albumin, found in egg white and blood, is a protein.
2. The answer is protein.

Teacher's Note:
1. Egg white is mostly albumin.
2. Keratin is another protein.

Answer: (a) CO₂, high

Explanation:
1. Carbon dioxide dissolves in water in larger amounts at high pressure.
2. Soft drinks are made by passing CO₂ under high pressure, and the gas fizzes out when the bottle is opened and the pressure drops.

Teacher's Note:
1. Gas solubility increases with pressure.
2. The bubbles when you open the bottle are CO₂.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. A is true: argon and krypton are inert gases, and they are used to fill bulbs.
2. R is true: argon keeps the hot tungsten filament from oxidising, and krypton reduces the sublimation of the filament.
3. These two roles are exactly why the gases are used, so R explains A: (a).

Teacher's Note:
1. Ask why an inert gas is put inside a bulb.
2. An inert gas does not react with the hot filament.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. A is true: gold threads are woven into silk sarees.
2. R is true: gold can be drawn into extremely thin wires.
3. Because of this ductility it can be made into threads, so R explains A: (a).

Teacher's Note:
1. To make a thread of a metal, the metal must be ductile.
2. Ductile means it can be drawn into wires.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. A is true: helium fills weather balloons.
2. R is true: helium is much lighter than air, so the balloon rises, and it is inert, so it does not catch fire.
3. These properties are why it is used, so R explains A: (a).

Teacher's Note:
1. Which properties make a gas safe and useful for balloons?
2. Hydrogen is lighter but burns.

Answer: (c) A is true, but R is false.

Explanation:
1. A is true: gold is used for jewellery and coins because of its lustre and resistance to chemicals.
2. R is false: gold is a soft metal, which is why it is alloyed with copper for jewellery.
3. So A is true and R is false: (c).

Teacher's Note:
1. Pure gold can be scratched easily.
2. Gold is valued for lustre, malleability and inertness.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. A is true: high-voltage transmission lines are made of aluminium.
2. R is true: aluminium conducts well, is light and does not corrode easily.
3. These properties are the reasons for its use, so R explains A: (a).

Teacher's Note:
1. Long wires must be light, conductive and weather-resistant.
2. Aluminium is cheaper than copper.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. A is true: bulbs are filled with argon.
2. R is true: argon is inert, so the hot tungsten filament does not oxidise and the bulb lasts longer.
3. R gives the reason for A: (a).

Teacher's Note:
1. An inert gas protects the filament.
2. Without it the filament would burn out quickly.

Answer: (c) A is true, but R is false.

Explanation:
1. A is true: duralumin is used for aircraft frames.
2. R is false: duralumin is light in weight and has a high tensile strength, which are the reasons it is used.
3. So A is true and R is false: (c).

Teacher's Note:
1. Aircraft need light and strong materials.
2. R states the opposite properties.

Answer: (c) A is true, but R is false.

Explanation:
1. A is true: graphite is used as a moderator in nuclear reactors.
2. R is false: graphite slows down the fast neutrons so that they can split more uranium atoms. It does not speed them up.
3. So A is true and R is false: (c).

Teacher's Note:
1. A moderator slows neutrons.
2. Slow neutrons are better at causing fission in uranium-235.