Which is the least polarizable gas among the following?

Which of the following is the most basic oxide?
(1) Al₂O₃

(2) Sb₂O₃

(3) Bi₂O₃

(4) SeO₂

Least stable hydride is:

(1) stannane 

(2) silane 

(3)  plumbane 

(4) germane

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 $\mathrm{HOCl}$

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