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

Acetophenone cannot be prepared easily starting from

Benzaldehyde can be formed by :-

Which one of the combinations will give propanaldehyde on dry distillation?

Identify product $B$ in the following reaction:
Benzonitrile $\xrightarrow[\text{Dry ether}]{C_6H_5MgBr} A$ $\xrightarrow{H_3O^{+}} B$

Describe the method of preparation of aldehydes from nitrile and ester compounds by reaction with $DIBAL-H$.