Which is best nucleophile in polar aprotic solvent?

The major products $\mathrm{A}$ and $\mathrm{B}$ in the following reactions are

Which of the following carbocations is most stable?

The correct statement regarding electrophiles is:

The following compound

can readily be prepared by Williamson ether synthesis by reaction between

Arrange the following carbanions in order of their decreasing stability

(i) ${\mathrm{H}}_3\mathrm{C}-\mathrm{C}\equiv {\mathrm{C}}^{-}$

(ii) $\mathrm{H}-\mathrm{C}\equiv {\mathrm{C}}^{-}$

(iii) ${\mathrm{H}}_3\mathrm{C}-{\mathrm{CH}}_2^{-}$

The indicated atom is not a nucleophilic site in

Choose the correct statement regarding the formation of carbocations A and B given :-

The stability order of the above carbocations is 

Which of the following statements is not correct for a nucleophile?