The reagent used for the Gatterman-Koch formylation of arene is

Which reagent is useful in the conversion of ethanenitrile to ethanal?

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

Identify the reagent used for the preparation of benzophenone from benzonitrile.

Identify the final product $A$ in the given reaction sequence.

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