How do aldehydes differ from ketones?

Aldehydes are defined by having a carbonyl group (C=O) positioned at the end of the carbon chain. This structural characteristic is what fundamentally differentiates aldehydes from ketones. In contrast, ketones have their carbonyl group located within the carbon chain, which means there is at least one carbon atom on either side of the carbonyl group. This is an important distinction because it influences the chemical properties and reactivity of these compounds.

The location of the carbonyl group in aldehydes makes them more reactive than ketones under certain conditions, particularly in nucleophilic addition reactions. Additionally, aldehydes can be oxidized to form carboxylic acids, while ketones cannot be easily oxidized due to their structure.

This understanding highlights why option B accurately describes the unique placement of the carbonyl group in aldehydes compared to ketones.