$[Figure]$ $\xrightarrow[{(ii){H_2}O}]{{(i)\,{C_2}{H_5}MgBr}}A\xrightarrow{{HCl}}B$
$CH _{3} CH _{2} CH = CH _{2}$ $\xrightarrow[{Rh\,\,catalyst}]{{{H_2}/CO}}$
$HC \equiv CH\mathop {\xrightarrow{{30\%\, {H_2}S{O_4}}}}\limits_{HgS{O_4}} A\xrightarrow{{NaOH}}B$