CBSE Class 8 Science Advanced Chemistry Synthetic Clothing Material and Polymer MCQs Set 02

Answer: (d) All

Explanation:
1. Metals, diamond and plastic do not decay by the action of micro-organisms.
2. So all three are non-biodegradable: All.

Teacher's Note:
1. Biodegradable wastes rot: food, paper, jute.
2. Metal cans may take 100 to 500 years to break down.

Answer: (c) Jute

Explanation:
1. Steel, nylon and stone are not decomposed by micro-organisms.
2. Jute is a plant fibre and rots, so the answer is jute.

Teacher's Note:
1. Natural materials are usually biodegradable and man-made ones are not.
2. Cotton cloth rots in a few months.

Answer: (b) Non-biodegradable

Explanation:
1. The old branched-chain synthetic detergents could not be broken down by micro-organisms.
2. They stayed in rivers and lakes and caused foam and pollution.
3. So they are non-biodegradable.

Teacher's Note:
1. Soaps are biodegradable, but the older synthetic detergents were not.
2. Modern detergents are made with straight chains to be biodegradable.

Answer: (b) not broken down easily by natural process

Explanation:
1. 'Bio' means life and 'degradable' means able to be broken down.
2. Non-biodegradable materials are not broken down easily by natural processes.

Teacher's Note:
1. Add the word 'non' to flip the meaning.
2. Plastic, glass and metals are examples.

Answer: (d) a, b and c

Explanation:
1. Rayon is soft to wear.
2. It is shiny and silky like silk.
3. It absorbs moisture, so it absorbs sweat.
4. All three reasons are right: a, b and c.

Teacher's Note:
1. Tick each reason separately.
2. Moisture absorption makes rayon comfortable in summer.

Answer: (b) Polywool

Explanation:
1. Cotton is a single natural fibre; rayon and nylon are single fibres made from one material.
2. Polywool is a mixture of polyester and wool, so it is a blended fabric: Polywool.

Teacher's Note:
1. A blend has two names joined together.
2. Examples: polycot, terrywool, cotswool.

Answer: (c) thermosetting plastic.

Explanation:
1. A saucepan handle must not soften when heated.
2. Thermosetting plastics such as Bakelite do not melt once set and are poor conductors of heat.
3. So the handles are made of thermosetting plastic.

Teacher's Note:
1. Thermoplastics would soften near the flame.
2. Bakelite handle activity: it stays cool to touch.

Answer: (a) wool < cotton < silk < nylon

Explanation:
1. In the tensile-strength activity the weights needed to break the threads were: wool the least, cotton 75 g, silk 150 g and nylon 375 g.
2. The increasing order is therefore wool < cotton < silk < nylon.
3. This is option (a).

Teacher's Note:
1. Larger breaking weight means a stronger thread.
2. Nylon is always the strongest of the four.

Answer: (c) Light, strong and remouldable

Explanation:
1. Plastics are poor conductors, not good ones, and they do not react with air or water.
2. Malleable is a property of metals.
3. Plastics are light, strong and can be moulded again and again: (c).

Teacher's Note:
1. Each wrong option names a property plastics do not have.
2. Lightness and strength make plastics so handy.

Answer: (c) Polyester

Explanation:
1. Polyester is made from two monomers and it is strong and durable.
2. It is used for curtains and, as mylar film, for magnetic recording tapes.
3. It has two common names, Terylene and Dacron.
4. The fabric is polyester.

Teacher's Note:
1. Terylene and Dacron are the two names.
2. Rayon and acrylic are not made from two monomers.

Answer: (d) All of the above

Explanation:
1. Blending natural fibre with a cheaper synthetic fibre lowers the cost.
2. The blend keeps the good properties of both fibres.
3. The blend is made by mixing the two kinds of fibre, so all statements are accepted: all of the above.

Teacher's Note:
1. A blend combines the comfort of natural fibres with the strength of synthetic ones.
2. Terrycot and polycot are examples.

Answer: (d) wood pulp

Explanation:
1. Silk comes from the cocoon, but rayon is not made from it.
2. Rayon is made by treating wood pulp (cellulose) with chemicals to get viscose.
3. So rayon is obtained from wood pulp.

Teacher's Note:
1. Rayon is semi-synthetic: it starts from a natural material.
2. Petroleum gives fibres like nylon and polyester.

Answer: (b) acrylic

Explanation:
1. Rayon looks like silk, and polycot is polyester blended with cotton.
2. Acrylic resembles wool and is used in its place, so it is the artificial wool: acrylic.

Teacher's Note:
1. Rayon is artificial silk; acrylic is artificial wool.
2. Orlon and Acrilan are other names for acrylic.

Answer: (c) Polyester

Explanation:
1. Cloth dries fast if it absorbs very little water.
2. Polyester absorbs very little water, so it dries quickly after washing.
3. The answer is polyester.

Teacher's Note:
1. Rayon, wool and silk soak up more water.
2. This is why polyester is called a wash-and-wear fabric.

Answer: (b) Cotton

Explanation:
1. Synthetic fibres melt easily and stick to the skin if they catch fire.
2. Rayon is semi-synthetic and burns vigorously, and polycot contains polyester.
3. Cotton does not melt, so it is the safest: cotton.

Teacher's Note:
1. Avoid synthetic clothes near flames.
2. Pure cotton is the usual advice for the kitchen and laboratory.

Answer: (b) Thermoplastics are good conductor of heat and electricity

Explanation:
1. All plastics, thermosetting or thermoplastic, are poor conductors of heat and electricity.
2. So the statement that thermoplastics are good conductors is false: (b).

Teacher's Note:
1. For 'NOT true' questions, test each statement and pick the false one.
2. Plastics are used to cover electric wires because they do not conduct.

Answer: (d) all of the above

Explanation:
1. Plastics do not corrode, and they are easily moulded.
2. Some plastics, such as melamine, are flame resistant.
3. Since each property belongs to plastics, the answer is all of the above.

Teacher's Note:
1. Most plastics catch fire; melamine is the fire-proof exception.
2. When all options fit, choose 'all of the above'.

Answer: (d) Plastic

Explanation:
1. The 4 R's are reduce, reuse, recycle and recover.
2. Plastic is non-biodegradable and piles up as waste, so these four steps matter most for it: plastic.

Teacher's Note:
1. Reducing plastic use is the first step.
2. Cotton or jute bags can replace plastic bags.

Answer: (c) tin can

Explanation:
1. Paper takes 10 to 30 days and cotton cloth 2 to 5 months.
2. Plastic bags take several years, but metal cans such as tin take 100 to 500 years.
3. So the longest is the tin can.

Teacher's Note:
1. Compare the time ranges given in the notes.
2. Plastic bags are not the slowest here, though they are a bigger problem for animals.

Answer: (c) Its fabric melts and sticks to the body, in case of fire

Explanation:
1. Synthetic fibres melt very easily when they meet a flame.
2. If the cloth catches fire, the molten fabric sticks to the skin and causes severe burns.
3. So the reason is option (c).

Teacher's Note:
1. Discomfort is true but it is not the safety reason.
2. Same reason for wearing cotton in the laboratory.

Answer: (b) (i)-(r); (ii)-(p); (iii)-(s); (iv)-(q)

Explanation:
1. (i) Made from cellulose: rayon (r).
2. (ii) Used for woollen-type clothes: acrylic (p).
3. (iii) Thermosetting plastic: Bakelite (s).
4. (iv) Ropes and fishing nets: nylon (q).
5. This is the code (i)-(r); (ii)-(p); (iii)-(s); (iv)-(q), option (b).

Teacher's Note:
1. Match the sure pairs first, then eliminate options.
2. Nylon is strong and elastic, hence ropes and nets.

Answer: (b) Nylon

Explanation:
1. Wool and silk are of animal origin and smell like burning hair; cotton smells like burning paper.
2. A plastic-like smell shows a synthetic fibre, and of the options only nylon is synthetic.
3. So the dupatta is made of nylon.

Teacher's Note:
1. Use the smell test: hair means wool or silk, paper means cotton or rayon.
2. Synthetic fibres melt and give a chemical or plastic smell.

Answer: (d) Option (D)

Explanation:
1. X coats non-stick utensils: Teflon.
2. Y coats fire-fighters' uniforms: melamine.
3. Z is a polyester used for bottles and films: PET.
4. So X, Y, Z are Teflon, melamine and PET, which is option (D).

Teacher's Note:
1. PET stands for polyethylene terephthalate, a polyester.
2. Check each riddle against the properties in the notes.

Answer: (c) (a)-(iii), (b)-(iv), (c)-(v), (d)-(ii), (e)-(i)

Explanation:
1. (a) Toothbrush bristles are made of nylon: (iii).
2. (c) Bottles are made of PET: (v).
3. (e) Fire-resistant fabric uses melamine: (i).
4. Carpet matches rayon (iv) and toy matches PVC (ii) among the remaining items.
5. Only option (c) has (a)-(iii), (c)-(v) and (e)-(i), so the answer is option (c).

Teacher's Note:
1. Fix the three sure matches, then see which option agrees.
2. Do not waste time on the uncertain pairs if the sure ones decide the answer.

Answer: (d) Nylon, cotton, rayon and polyester.

Explanation:
1. W is strong, elastic and forms beads on melting: nylon.
2. X leaves almost no residue: cotton.
3. Y looks like silk and smells like burning paper: rayon.
4. Z does not wrinkle and burns with black smoke: polyester.
5. So W, X, Y, Z = nylon, cotton, rayon, polyester: option (d).

Teacher's Note:
1. Use the flame-test table from the notes.
2. Bakelite, melamine and PVC are plastics, not fibres, so options (b) and (c) fall at once.