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Q:

In addition to nitric acid, another acid which may render iron passive is 

A) acetic acid B) oxalic acid
C) chromic acid D) citric acid
 
Answer & Explanation Answer: C) chromic acid

Explanation:

Passivity of iron is due to formation of an extremely thin and impervious film of ferrosoferric oxide Fe3O4on the surface of iron. Chromic acid, being a powerful oxidising agent (like nitric acid ) renders iron passive. 

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Q:

Which of the following is used to preserve specimens in the biology laboratory?

A) Phenol B) Benzaldehyde
C) Formaldehyde D) Acetic acid
 
Answer & Explanation Answer: C) Formaldehyde

Explanation:

A 40% solution of Formaldehyde known as Formalin is used in the preservation of biological specimens because of its hardening action on proteins. 

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Q:

PAS  is a drug used in the treatment of 

A) tuberculosis B) Cancer
C) typhoid D) malaria
 
Answer & Explanation Answer: A) tuberculosis

Explanation:

Para-amino salicyclic acid (PAS) is used in the treatment of Tuberculosis.

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Q:

Heated saw dust catches fire when a drop of concentrated nitric acid is added to it. This is due to

A) dehydration B) oxidation
C) reduction D) dehydrogenation
 
Answer & Explanation Answer: B) oxidation

Explanation:

Saw dust contains carbon which is oxidised to carbon  dioxide by concentrated nitric acid;

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Q:

Which of the following is a regenerated fibre?

A) Terylene B) Rayon
C) Nylon D) Silk
 
Answer & Explanation Answer: B) Rayon

Explanation:

Terylene and nylon are synthetic fibres produced by a process of polymerisation. Terylene is a polyester and nylon, a poyamide.

Silk is purely a natural product obtained from silk worms.

Rayon is a man-made material which consists of purified cellulose in the form of long fibres. Cellulose occurs in the cell wall of plants. Rayon fibre is chemically identical to cotton but has a shine like silk. Since it is  basically derived from a natural source (cellulose) it is called a regenerated fibre.

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Q:

Which of the following carbon compounds is used as a fire- extinguisher?

A) Carbon disulphide B) Chloroform
C) Carbon tetrachloride D) Methyl ene chloride
 
Answer & Explanation Answer: C) Carbon tetrachloride

Explanation:

Vapour of carbon tetra chloride ccl4 is non-inflammable and is heavier than air. Hence it is used as a fire extinguisher under the trade name of pyrene.

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Q:

If people sleep in closed rooms where charcoal fire is burning , they die due to 

A) carbon monoxide B) carbon dioxide
C) methane D) phosgene
 
Answer & Explanation Answer: A) carbon monoxide

Explanation:

A closed room is aplace where charcoal is burnt in limited supply of air. There is every chance for the formation of the deadly poisonous carbon monoxide, which when inhaled, reacts with the iron in haemoglobin of blood and prevents the supply of oxygen. It is said to be treacherous as there can be no previous warning of its presence because it is an odourless and colourless gas.

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Q:

One method by which the components of air can be seperated is 

A) shaking with caustic soda solution B) shaking with water
C) fractional distillation of liquid air D) passing air over heated magnesium
 
Answer & Explanation Answer: C) fractional distillation of liquid air

Explanation:

The two main components of air are nitrogen and oxygen. They are seperated by the fractional distillation of liquid air. Liquefied air contains liquid nitrogen and liquid oxygen. Liquid nitrogen with the lower boiling point more readily evaporates than the less volatile liquid oxygen. 

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