Nitrogen form $N_2$, but phosphorous  form $P_2$, it's at a time convert in $P_4$, reason is:

1. Triple bond present between phosphorous atoms. 
2. $\mathrm{p}\mathrm{\pi }-p\mathrm{\pi }$ bonding is weak in phosphorous.
3. $\mathrm{p}\mathrm{\pi }-p\mathrm{\pi }$ bonding is strong in phosphorous.
4. Multiple bonds easily form phosphorous.

NH₃ forms a hydrogen bond but PH₃ does not because:  

Nitrogen exists as a diatomic molecule and phosphorus as P₄ because on moving 

A chemical that depletes the ozone layer is:

1. Sulphur

2. Chlorofluorocarbons (CFCs)

3. Nitrogen

4. Hydrogen

Fluorine forms only one oxoacid, HOF because of -

1. Low electronegativity and small size

2. High electronegativity and small size

3. High electronegativity and big size

4. Low electronegativity and big size

Oxygen forms hydrogen bonds while chlorine does not, because :

The uses of ${\mathrm{ClO}}_2$ is /are-

1. It is used for purifying water

2. It is used as a bleaching agent

3. Both '1'and '2'

4. None of the above

Halogens are colored because -

1. They absorb radiations in the U.V region

2. They absorb radiations in the visible region

3. They absorb radiations in the infrared region

4. They absorb radiations in the radiowaves region

 4HCl + O₂ →  X + 2H₂O

Cl₂ + H₂O → HCl  + Y ;

X and Y in the above reaction are respectively:

1.  Cl₂ , HOCl

2. HOCl ,Cl₂

3. HClO₃, HOCl

4. HOCl, HClO₄

A neutral molecule that is isoelectronic with ClO^- is -

1. ClF which is a Lewis base

2. ClF which is a Lewis acid

3. HCl which is a Lewis base

4. HCl which is a Lewis acid