The typical reaction of an aldehyde is

Which of the following does not reduce Fehling solution?

The given reaction is: $R_2C=O + HCN \rightarrow R_2C(OH)CN$

The major product $(P)$ in the following reaction is :

The aldehydes which will not form a single Grignard product with one equivalent of Grignard reagent are:
$(a)$ Benzaldehyde
$(b)$ $4$-Formylbenzoic acid
$(c)$ $4$-Methoxybenzaldehyde
$(d)$ $4$-(Hydroxymethyl)benzaldehyde

Schiff's base is prepared from: