Catalyst used in Rosenmund reduction is

Dry distillation of a mixture of calcium acetate and calcium formate forms:

Which of the following reactions will produce $R-CO-Ar$?

$Ph - C \equiv C - CH_3 \xrightarrow{Hg^{2+}/H^+} A$. What is $A$?

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

Which of the following reactions cannot be used to prepare Benzaldehyde?