Hydrogen is evolved by the action of cold dilute HNO₃ on:

1. Fe

2. Mg or Mn

3. Cu

. Al

The lightest gas is :

1. nitrogen

2. helium

3. oxygen

4. hydrogen

Atomic hydrogen is obtained by:

1. electrolysis of heavy water

2. reaction of water with heavy metals

3. thermal decomposition of water

4. passing silent electric discharge through hydrogen at low pressure

Hydrogen is not obtained when zinc reacts with:

1. cold water

2. dil. H₂SO₄

3. dil HCl

4. hot 20% NaOH

Para hydrogen at room temperature is:

1. Less stable than ortho hydrogen.

2. More stable than ortho hydrogen.

3. As stable as ortho hydrogen.

4. None of the above.