Which of the following compounds is most reactive towards nucleophilic attack on the carbonyl group?

The synthesis of crotonaldehyde from acetaldehyde is an example of ....... reaction.

What is the product of the following reaction?

The reaction of ethyl methyl ketone with $Cl_2$ / excess $OH^{-}$ gives the following major product:

Consider the following sequence of reactions:
Ketone $A$ $\xrightarrow[2. H_2O]{1. C_2H_5MgBr} B$ $\xrightarrow[- H_2O]{H_2SO_4, \text{Heat}} C$ $\xrightarrow[2. Zn, H_2O]{1. O_3} \text{Propanone} + \text{Acetaldehyde}$
The ketone $A$ is:

The major product of the following reaction is: