$PC{l}_5$ exists but $NC{l}_5$ does not because:

1. Nitrogen has no vacant d-subshells .

2. $NC{l}_5$ is unstable .

3. Nitrogen atom is much smaller than p .

4. Nitrogen is highly inert . 

The correct order of acidic strength is :

1. ${\mathrm{Cl}}_2{\mathrm{O}}_7>{\mathrm{SO}}_2>{\mathrm{P}}_4{\mathrm{O}}_{10}$                   

2. ${\mathrm{CO}}_2>{\mathrm{N}}_2{\mathrm{O}}_5>{\mathrm{SO}}_3$

3. ${\mathrm{Na}}_2\mathrm{O}>\mathrm{MgO}>{\mathrm{Al}}_2{\mathrm{O}}_3$                   

4. ${\mathrm{K}}_2\mathrm{O}>\mathrm{CaO}>\mathrm{MgO}$

Which is the least polarizable gas among the following?

O$—$O bond length ($\mathrm{in} \stackrel{°}{\mathrm{A}}$ ) in  $H_2{O}_2$ and $O_2{F}_2$ is respectively:

The correct statement about hydrolysis of ${\mathrm{BCl}}_3$ and ${\mathrm{NCl}}_3$ is-

1. ${\mathrm{NCl}}_3$ is hydrolysed and gives $\mathrm{HOCl}$ but ${\mathrm{BCl}}_3$ is not hydrolysed

2. Both ${\mathrm{NCl}}_3$ and ${\mathrm{BCl}}_3$ on hydrolysis gives $\mathrm{HCl}$

3. ${\mathrm{NCl}}_3$ on hydrolysis gives $\mathrm{HOCl}$  but ${\mathrm{BCl}}_3$ gives $\mathrm{HCl}$

4. Both ${\mathrm{NCl}}_3$ and ${\mathrm{BCl}}_3$ on hydrolysis gives $\mathrm{HOCl}$

The correct order of solubility in an aqueous medium is: 

1. CuS > ZnS > Na₂S

2. ZnS > Na₂S > CuS

3. Na₂S > CuS > ZnS

4. Na₂S > ZnS > CuS