Which is the least polarizable gas among the following?

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

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-

Select correct statement(s) :

(1) Acidic strength of $\mathrm{HBr}>\mathrm{HCl}$ but reverse is true for their reducing property 

(2) Basic strength of ${\mathrm{PH}}_3>{\mathrm{AsH}}_3$ but reverse is true for their bond angle

(3) Dipole moment of ${\mathrm{CH}}_3\mathrm{Cl}>{\mathrm{CH}}_3\mathrm{F}$ but reverse is true for their $\mathrm{H}\hat{\mathrm{C}}\mathrm{H}$ bond angle

(4) ${\mathrm{K}}_{{\mathrm{a}}_1}$ of fumaric acid is higher than maleic acid but reverse is true for their ${\mathrm{K}}_{{\mathrm{a}}_2}$

O$—$O bond length ($\mathrm{in}<mspace\; width="1em"></mspace>\stackrel{°}{\mathrm{A}}$ ) in  $H_2{O}_2$ and $O_2{F}_2$ is respectively:

Cis-butene dioic acid $\stackrel{{\mathrm{K}}_{{\mathrm{a}}_1}\{-{\mathrm{H}}^{+}\}}{\rightleftharpoons }{{\mathrm{X}}^{-}}_1\stackrel{{\mathrm{K}}_{{\mathrm{a}}_2}\{-{\mathrm{H}}^{+}\}}{\rightleftharpoons }{\mathrm{X}}_2^{2-}$

Trans-butene dioic acid $\stackrel{{\mathrm{K}}_{{\mathrm{a}}_1}\text{'}\{-{\mathrm{H}}^{+}\}}{\rightleftharpoons }{{\mathrm{Y}}^{-}}_1\stackrel{{\mathrm{K}}_{{\mathrm{a}}_2}·\{-{\mathrm{H}}^{+}\}}{\rightleftharpoons }{\mathrm{Y}}_2^{2-}$

The incorrect statement regarding above the information is:

(1) ${\mathrm{X}}_2^{2-}$ species is more basic than ${\mathrm{Y}}_2^{2-}$ species 

(2) ${\mathrm{X}}_1^{-}$ species is more basic than ${\mathrm{Y}}_1^{-}$ species

(3) ${\mathrm{K}}_{\mathrm{a}1}$ is greater than $\mathrm{K}{\text{'}}_{\mathrm{a}2}$ 

(4) $\mathrm{K}{\text{'}}_{\mathrm{a}2}$ is greater than $\mathrm{K}{\text{'}}_{\mathrm{a}2}$

$PC{l}_5$ 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 . 

Select the most ionic and most covalent compounds respectively from the following.

$Cr{O}_5,M{n}_2{O}_7,PbO,<mspace\; width="1em"></mspace>P_4{O}_{10},<mspace\; width="1em"></mspace>Sn{O}_2$

(A) $Cr{O}_5,<mspace\; width="1em"></mspace>M{n}_2{O}_7$                                (B)  $PbO,<mspace\; width="1em"></mspace>M{n}_2{O}_7$

(C) $Cr{O}_5,<mspace\; width="1em"></mspace>P_4{O}_{10}$                                 (D) $Sn{O}_2,<mspace\; width="1em"></mspace>Cr{O}_5$