CBSE Class 7 Science Advanced Chemistry Chemistry in Daily Life MCQs Set 02

Answer: (d) zinc

Explanation:
1. Copper, silver and aluminium are good electrical conductors.
2. Zinc is brittle, so it is not used, and the answer is zinc.

Teacher's Note:
1. Printed circuits are usually copper.
2. Brittleness makes zinc unsuitable for thin conducting tracks.

Answer: (c) it is soft in nature

Explanation:
1. A pencil must leave a mark on paper.
2. Graphite is soft and leaves an impression on paper, so the answer is it is soft in nature.

Teacher's Note:
1. Other properties of graphite are true but do not explain writing.
2. Softness is the property that matters for pencil leads.

Answer: (d) argon

Explanation:
1. Balloons need a gas lighter than air.
2. Helium, neon and hydrogen are lighter than air, but argon is heavier than air.
3. So the answer is argon.

Teacher's Note:
1. A balloon rises only if its gas is lighter than air.
2. Argon is used in bulbs instead.

Answer: (a) superphosphate of lime (calcium dihydrogen phosphate with gypsum)

Explanation:
1. Nitre (potassium nitrate), ammonium sulphate and triammonium phosphate all contain nitrogen.
2. Superphosphate of lime has no nitrogen, so the answer is superphosphate of lime.

Teacher's Note:
1. Look for nitrogen in the formula (nitrate, ammonium, urea).
2. Superphosphate supplies phosphorus only.

Answer: (b) A – e, B – a, C – b, D – c

Explanation:
1. Hydrochloric acid cleans bathrooms (e).
2. Hydrated copper sulphate is sprayed over grape vines (a).
3. Limestone/marble is used for floors, statues and monuments (b).
4. Zincite (zinc oxide) is used in paints (c).
5. So the match is A – e, B – a, C – b, D – c.

Teacher's Note:
1. Match the sure ones first and eliminate options.
2. Hydrated copper sulphate is also called blue vitriol.

Answer: (a) 321465

Explanation:
1. Mix the main raw materials (3), add cullet (2) and the special ingredients (1).
2. Melt in the furnace (4), blow the glass (6) and finally anneal (5).
3. The order is 321465.

Teacher's Note:
1. Shaping (blowing) comes after melting and before annealing.
2. Remember: raw materials, cullet, additives, melt, shape, anneal.

Answer: (d) copper

Explanation:
1. A cable must conduct electricity very well.
2. Of the four metals, copper has the highest electrical conductivity, so the answer is copper.

Teacher's Note:
1. Think about conductivity, not cost or weight.
2. Silver is better but too costly.

Answer: (d) 4213

Explanation:
1. Collect sea water (4) and evaporate it (2).
2. Dissolve the crude salt to make a hot saturated solution (1).
3. Cool to recrystallize (3).
4. The suitable sequence is 4213; the iodide addition is a step of making table salt and is not part of getting sodium chloride itself.

Teacher's Note:
1. Sodium chloride is the pure salt; iodides are added later for table salt.
2. So drop step 5 from the sequence.

Answer: (d) radon

Explanation:
1. Argon, neon and others are inert and safe in bulbs.
2. Radon is radioactive, so radon cannot be used.

Teacher's Note:
1. Radioactive radiation would be harmful.
2. Radon is used in cancer treatment instead.

Answer: (a) silicon carbide because it is the hardest substance

Explanation:
1. Grinding wheels have to cut other hard materials.
2. Silicon carbide, the hardest compound, is used, so the answer is silicon carbide because it is the hardest substance.

Teacher's Note:
1. Hardness is the key property for grinding.
2. Ferrosilicon is a hard steel but is not the one used for wheels.

Answer: (b) poor electrical conductivity

Explanation:
1. A pan must resist heat and chemicals and must not stick.
2. Electrical conductivity is not relevant to cookware, so the answer is poor electrical conductivity.

Teacher's Note:
1. Try each property with a frying pan in mind.
2. Poor conductivity is used for electrical insulators.

Answer: (d) All the above

Explanation:
1. Thermoplastics can be reshaped again and again without chemical change.
2. Thermosetting plastics harden for ever once set.
3. All three statements are correct: all the above.

Teacher's Note:
1. Use the memory aid: thermoplastic means remould, thermosetting means fixed.
2. Each of the three options is correct.

Answer: (c) 1 3 2 4

Explanation:
1. Methane \(\ce{CH4}\) has 1 carbon; glucose \(\ce{C6H12O6}\) has 6; sugar \(\ce{C12H22O11}\) has 12; starch \(\ce{(C6H10O5)_n}\) has 6n.
2. The order is methane, glucose, sugar, starch: 1 3 2 4.

Teacher's Note:
1. Write each formula first and count the carbon.
2. Starch is a long polymer so it has the most carbon atoms.

Answer: (d) argon

Explanation:
1. The gas must be lighter than air.
2. Argon is heavier than air, so the answer is argon.

Teacher's Note:
1. Helium is preferred because it is light and non-flammable.
2. Argon is better suited for filling bulbs.

Answer: (b) A → e, B → a, C → b, D → c

Explanation:
1. Hydrochloric acid: bathroom cleaner (e).
2. Hydrated copper sulphate: sprayed over grape vines (a).
3. Limestone: floors, statues, monuments (b).
4. Zincite: paints (c).
5. The match is A → e, B → a, C → b, D → c.

Teacher's Note:
1. Begin with the entry you are surest about.
2. Use elimination on the options.

Answer: (a) glycerine

Explanation:
1. Oil reacts with sodium hydroxide to form soap and glycerine.
2. The by-product is glycerine.

Teacher's Note:
1. The main product is the soap.
2. Glycerine is useful in other products.

Answer: (d) zinc

Explanation:
1. Printed circuits need good conductors that can be shaped.
2. Zinc is brittle, so zinc cannot be used.

Teacher's Note:
1. Copper is the usual metal here.
2. Brittle metals break when made into thin tracks.

Answer: (a) vegetable oil

Explanation:
1. Fats give more energy than carbohydrates or proteins.
2. So the answer is vegetable oil.

Teacher's Note:
1. Glucose is quick, fat is large.
2. Cereals are mostly carbohydrates.

Answer: (a) increases the hardness of gold

Explanation:
1. Pure gold is soft and gets scratched or bent easily.
2. Alloyed gold is harder and more impact resistant, so the answer is increases the hardness of gold.
3. Alloyed gold also melts more easily, so (d) is wrong.

Teacher's Note:
1. Ornaments must keep their shape in use.
2. Alloying makes gold harder, not softer.

Answer: (c) potassium bisulphate

Explanation:
1. Potassium nitrate gives potassium and nitrogen.
2. Triammonium phosphate gives nitrogen and phosphorus.
3. Potassium bisulphate gives only potassium, so the answer is potassium bisulphate.

Teacher's Note:
1. Count the nutrients in each formula.
2. Look for ammonium or nitrate (nitrogen) and phosphate (phosphorus).

Answer: (b) 2 1 3 4

Explanation:
1. Mixing (2) comes first, then pulverizing (1).
2. Heating forms clinkers (3), then grinding with gypsum (4).
3. The order is 2 1 3 4.

Teacher's Note:
1. Write the story of cement in your own words to remember it.
2. Gypsum is added last.

Answer: (c) it is soft

Explanation:
1. A pencil leaves a mark when a soft material rubs on paper.
2. Graphite is soft, so the answer is it is soft.

Teacher's Note:
1. Pencil hardness depends on how much clay is mixed in.
2. Only softness is related to writing.

Answer: (a) cement mortar

Explanation:
1. Plastering needs a fine paste of cement and sand.
2. So the answer is cement mortar.

Teacher's Note:
1. Concrete and RCC contain gravel or steel.
2. Mortar also joins bricks.

Answer: (a) silicon carbide because it is the hardest substance

Explanation:
1. A grinding wheel must be harder than the material it cuts.
2. Silicon carbide is the hardest compound of silicon, so the answer is silicon carbide.

Teacher's Note:
1. Match the property to the use.
2. Hardness is the exploited property.

Answer: (d) bakelite

Explanation:
1. Polyethylene, nylon and terylene soften on heating and are thermoplastics.
2. Bakelite is thermosetting: bakelite.

Teacher's Note:
1. Bakelite is used in plug sockets and kitchen handles.
2. Thermosetting plastics cannot be remelted.

Answer: (d) 4 2 1 3

Explanation:
1. Collect sea water (4), evaporate it (2).
2. Make a hot saturated solution of the crude salt (1) and recrystallize (3).
3. Iodide addition is for table salt, so it is not in the relevant steps.
4. The sequence is 4 2 1 3.

Teacher's Note:
1. The word 'relevant' tells you to leave out the iodide step.
2. Recrystallization is the last purification step.

Answer: (d) radon

Explanation:
1. Radon is radioactive and so cannot be used in bulbs.
2. The answer is radon.

Teacher's Note:
1. Radioactive substances emit harmful radiation.
2. Radon is used in cancer treatment.

Answer: (c) A → c, B → d, C → e, D → a

Explanation:
1. Metal cleaning: HCl (c).
2. Insecticide: copper sulphate pentahydrate (d).
3. Taj Mahal: marble, \(\ce{CaCO3}\) (e).
4. Casting: plaster of Paris (a).
5. The match is A → c, B → d, C → e, D → a.

Teacher's Note:
1. Take each use and recall the compound.
2. Marble is chemically calcium carbonate.

Answer: (c) sodium lauryl sulphate

Explanation:
1. Soaps form scum in hard water.
2. Sodium lauryl sulphate is a detergent that does not form scum: sodium lauryl sulphate.

Teacher's Note:
1. Detergents are the answer to the hard water problem.
2. Both sodium and potassium soaps give scum.

Answer: (d) copper

Explanation:
1. Cables need excellent electrical conductivity.
2. Copper is the best of these, so the answer is copper.

Teacher's Note:
1. Aluminium is lighter but less conducting.
2. Iron and tin conduct poorly.

Answer: (a) a solution of glucose

Explanation:
1. Glucose is simple and is absorbed directly.
2. The answer is a solution of glucose.

Teacher's Note:
1. This is why athletes drink glucose water.
2. Complex foods must be digested first.

Answer: (d) making electric transmission cables

Explanation:
1. Alloys are used for statues, utensils and shells.
2. Cables need pure copper for best conductivity: making electric transmission cables.

Teacher's Note:
1. Impurities lower electrical conductivity.
2. So cables use refined copper.

Answer: (a) superphosphate of lime (calcium dihydrogen phosphate with gypsum)

Explanation:
1. Nitre, ammonium sulphate and triammonium phosphate contain nitrogen.
2. Superphosphate of lime has none: superphosphate of lime.

Teacher's Note:
1. Check for nitrate or ammonium in the name.
2. Superphosphate supplies phosphorus.

Answer: (a) 3 2 1 4 6 5

Explanation:
1. Mix raw materials (3), add cullet (2), add special ingredients (1).
2. Melt (4), blow (6), anneal (5).
3. The order is 3 2 1 4 6 5.

Teacher's Note:
1. Shaping comes after melting.
2. Annealing comes last.

Answer: (b) soft nature

Explanation:
1. Crucibles use chemical resistance and high melting point.
2. Electrodes use electrical conductivity.
3. Softness is not used: soft nature.

Teacher's Note:
1. Pencil lead is where softness is used.
2. Match each property to its use.

Answer: (c) RCC

Explanation:
1. A pillar must bear heavy loads.
2. RCC is the strongest: RCC.

Teacher's Note:
1. RCC means reinforced cement concrete.
2. Steel bars give the extra strength.

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

Explanation:
1. Assertion: the fusible alloy of lead and tin in equal masses is used for fuse wire. This is true.
2. Reason: lead and tin both melt at low temperatures, which is true.
3. A fuse wire must melt quickly when the current is too high, and the low melting points explain this: both true and R explains A.

Teacher's Note:
1. A fuse protects a circuit by melting.
2. Link the use (fuse) with the property (low melting point).

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

Explanation:
1. Assertion: gold is used for jewellery and coins, which is true.
2. Reason: gold is a relatively soft metal, so the statement 'hard' is false.
3. So A is true but R is false.

Teacher's Note:
1. Gold is chosen for its shine, malleability and resistance to chemicals.
2. That is why it is alloyed with copper or silver to harden it.

Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Explanation:
1. Assertion: tin is used in fusible alloys because it has a low melting point. This is true.
2. Reason: tin is a metal and a conductor of electricity, so it is true as given in the book.
3. But the conductivity does not explain the use, so both are true but R is not the correct explanation.

Teacher's Note:
1. The real reason for the use is the low melting point.
2. Check whether the reason explains the assertion, not just whether it is true.

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

Explanation:
1. Assertion: gold threads are woven in silk sarees, which is true.
2. Reason: gold is highly ductile, so it can be drawn into very fine threads.
3. The reason explains the assertion: both true and R explains A.

Teacher's Note:
1. Ductile means can be drawn into wires.
2. Gold can make extremely thin wire.

Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Explanation:
1. Tin has a low melting point, so it is used in fusible alloys (true).
2. It also conducts electricity (true as given), but this does not explain the use.
3. So both true but R is not the correct explanation.

Teacher's Note:
1. Assertion-reason questions test the link between the two statements.
2. Ask: does the reason cause the assertion?

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

Explanation:
1. Gold is used for jewellery and coins (true).
2. Gold is relatively soft, not hard (R is false).
3. So A is true but R is false.

Teacher's Note:
1. Look at the properties of gold in the table.
2. Gold is soft, malleable and ductile.

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

Explanation:
1. Fuse wire is the lead-tin alloy in equal masses (true).
2. Both metals melt at low temperature (true), which is why the alloy melts easily when too much current flows.
3. So both are true and R explains A.

Teacher's Note:
1. The alloy must melt before the appliance is damaged.
2. Low melting point is the key property.