Rank the following compounds in order of increasing reactivity in nucleophilic addition

Aldehydes, as well as ketones, combine with nucleophiles at the carbonyl carbon. They also form enolates that combine with electrophiles at the $\alpha$ carbon.

Nucleophilic addition involves two steps that include the nucleophilic attack and protonation. In the first step, the electrophilic carbonyl is attacked by the nucleophile. The next step involves the protonation of oxygen with a negative charge leading to the formation of the addition product.

The ball and stick model can be converted to obtain the following structures

Skeletal structures of the different compounds

Both aldehydes and ketones get subjected to nucleophilic addition reactions. The nucleophilic attack occurs at the carbonyl carbon. The reactivity of the carbonyl group is inversely proportional to the R groups connected to it. The carbonyl compound will have less reactivity if more R groups are connected to it. The compounds can be arranged in the order of their increasing reactivity as follows:

Increasing order of reactivity of the given compounds