Which of the following reagents is used in Gatterman-Koch formylation of arene?

What is $(P)$ in the reaction given below?
$(P)$ $\xrightarrow[\text{(ii) } H_3O^{+}]{\text{(i) } CH_3MgBr} (R)$ $\xrightarrow[\text{(ii) } \Delta]{\text{(i) dil. } NaOH} \text{4-methylpent-3-en-2-one}$

Consider the following reactions:
$C_2H_2 + H_2O \xrightarrow[333 \ K]{Hg^{2+} / H^{+}} [X] \stackrel{\text{Isomerisation}}{\rightleftharpoons} Y$
$Y$ cannot be obtained from which of the following reactions?

Benzyl chloride when oxidised by $Pb(NO_3)_2$ gives

$1$-Phenylethanol can be prepared by the reaction of benzaldehyde with the product obtained in the reaction between

Identify product $A$ in the following reaction: $R-C \equiv N \xrightarrow[ii) H_{3}O^{+}]{i) DIBAl-H} A$