A compound P is heated in a test tube with sodium hydroxide solution. A red litmus paper held at the mouth of the test tube turns blue. Which of the following could compound P be?

1. zinc sulphate
2. copper sulphate
3. ferrous sulphate
4. ammonium sulphate

Which of the following would weigh the least?
(Atomic masses C=12, O=16, Na=23)

1. 2 gram atoms of oxygen
2. one mole of sodium
3. 22.4 litres of carbon dioxide at STP
4. 6.023 x 10²² atoms of carbon

Assertion (A): Dry hydrogen chloride gas is collected by the upward displacement of air.

Reason (R): Hydrogen chloride gas is lighter than air.

1. Both A and R are true and R is the correct explanation of A
2. Both A and R are true but R is not the correct explanation of A
3. A is true but R is false
4. A is false but R is true

The structures of four hydrocarbons are shown below:

How many isomers of butene are there?

1. 1
2. 2
3. 3
4. 4