Class 8 Science Chapter 3 MCQ

Since plastic takes several years to decompose, it is not environment friendly. It causes environmental pollution. Besides, the burning process in the synthetic material is quite slow and it does not get completely burnt easily. In the process it releases lots of poisonous fumes into the atmosphere causing air pollution.

Nylon It was the first fully synthetic fibre. Nylon fibre was strong, elastic and light. Nylon is also used for making parachutes and ropes for rock climbing. A nylon thread is actually stronger than a steel wire.

PET is “polyethylene terephthalate”. PET as a plastic is very light weight and is commonly used for making kitchen containers.

A polymer is a chain of many small units of monomer. A synthetic fibre is also a chain of small units joined together. Each small unit is actually a chemical substance. Many such small units combine to form a large single unit called a polymer. The word ‘polymer’ comes from two Greek words; “poly” meaning “many” and “mer” meaning “part/unit”. So, a polymer is made of many repeating units.

Plastics and synthetic both are non-biodegradable. Burning of plastics and synthetic fabrics produces lots of poisonous gases causing air pollution. So, it is not advised to burn plastic and synthetic fibres.

Nylon is fibre, PVC is thermoplastic, bakelite is thermosetting plastic.

Here, all these statements are correct. Hence, your answer will be option [D].

Plastics are non-reactive, light in weight and durable but they do not conduct electricity.

Here, all these statements are correct except option [A]. “Rayon” is prepared by using wood pulp. Rayon is also known as semi-synthetic fibre, because this fibre is obtained by chemical treatment of wood pulp. Hence, your answer will be option [A].

Here, all these statements are correct. Hence, your answer will be option [D].

Bakelite is used for making the handles of various cooking utensils because it is a poor conductor of heat and does not become soft on getting heated.

Cotton is a “Natural polymer” called cellulose. Cellulose is made up of a large number of glucose units. Hence, “Cellulose” is a natural polymer of cotton fibre.

Rayon resembles silk in appearance; therefore, rayon is also called artificial silk.

Nylon is another man-made fibre. In 1931, it was made without using any natural raw material (from plant or animal). Nylon is also used for making parachutes and ropes for rock climbing. A nylon thread is actually stronger than a steel wire.

Here, all the statements are correct. Hence, your answer will be option [D].

Melamine is a thermosetting plastic which when molded once, cannot be softened and by heating.

A “Polymer” is a chain of many small units of “monomer”. Rest of all are correct. Hence, your answer will be option [C].

Polyester do not stretch and do not rot in contact with water. Polyester is used for making sails of sailboat. The polyester sails are light and strong. The most important use of polyester is in making fabrics for sarees, dress materials and curtains.

A rayon fibre was obtained by chemical treatment of wood pulp. This fibre was called rayon or artificial silk. Although rayon is obtained from a natural source, wood pulp, yet it is a man-made fibre. It is cheaper than silk and can be woven like silk fibres.

There are some plastics which when moulded once, can-not be softened by heating. These are called thermosetting plastics. Two examples are “Bakelite” and “Melamine”. Bakelite is a poor conductor of heat and electricity. It is used for making electrical switches, handles of various utensils, etc. Melamine is a versatile material. It resists fire and can tolerate heat better than other plastics. It is used for making floor tiles, kitchenware and fabrics which resist fire.

A fibre was obtained by chemical treatment of wood pulp (cellulose). This fibre was called rayon or artificial silk. Polymers occur in nature also. Cotton is a polymer called cellulose. Cellulose is made up of a large number of glucose units.

Here, all the statements are correct. Hence, your answer will be option [D].

When you burn synthetic fibres you find that their behaviour is different from that of the natural fibres. You must have noticed that synthetic fibres melt on heating. This is actually a disadvantage of synthetic fibres. If the clothes catch fire, it can be disastrous. The fabric melts and sticks to the body of the person wearing it. We should, therefore, not wear synthetic clothes while working in the kitchen or in a laboratory.

If you consider the statements there is written that “…Another synthetic fibres C is made of a polymer D the which consists of a large number of glucose units joined one after the other” it implies that “Fibre C” is prepared from the natural raw material.

Nylon is a synthetic fibre. It is made without using any natural raw material. Cotton, jute and wool are natural fibres.