Which of the following has highest reactivity towards nucleophilic substitution reaction involving cleavage of $\mathrm{C}-\mathrm{Cl}$ bond?

In a reaction,

$$ \left(\mathrm{CH}_3\right)_2 \mathrm{CHMgBr}+\mathrm{CO}_2 \xrightarrow[\text { ether }]{\text { dry }} \mathrm{A} \xrightarrow[\text { dilHCl }]{\mathrm{H} . \mathrm{OH}} \mathrm{~B} \text {. } $$

Find the product ' B ' of above reaction.

$$ \begin{aligned} & \text { If } \mathrm{E}^{\circ}\left(\mathrm{Fe}_{(\mathrm{aq})}^{+2} \mid \mathrm{Fe}_{(\mathrm{s})}\right)=-0.44 \mathrm{~V} \text { and } \\ & \mathrm{E}^{\circ}\left(\mathrm{Sn}_{(\mathrm{aq})}^{+2} \mid \mathrm{Sn}_{(\mathrm{s})}\right)=-0.14 \mathrm{~V} \end{aligned} $$

What is standard emf of cell containing the two electrodes?

Which of the following molecules contains maximum number of electrons in antibonding molecular orbitals?