The compounds A and B in the following reaction are, respectively

The reactants in the following reaction are A = Benzyl chloride and B = Benzyl isocyanide. The product of this reaction is benzyl isocyanide.
${\mathrm{C}}_6{\mathrm{H}}_6+ \mathrm{HCHO} \stackrel{\mathrm{HCl}}{\to }{\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{CH}}_2\mathrm{Cl} +{\mathrm{H}}_2\mathrm{O}$

${\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{CH}}_2\mathrm{Cl} +\mathrm{AgCN}\to {\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{CH}}_2\mathrm{NC} +\mathrm{AgCl}$