B is the right answer because dehydrogenation of secondary alcohol gives ketones nd tertiary alcohol gives alkenes . REFER TO NCERT CHEMISTRY BOOK CLASS 12 CHAPTER ALCOHOL PHENOL AND ETHER .

Explanation:

To understand why the dehydrogenation of secondary alcohols cannot produce aldehydes, let's first understand what dehydrogenation is and how it occurs in alcohols.

Dehydrogenation:
Dehydrogenation is a chemical reaction that involves the loss of hydrogen atoms from a molecule. In the case of alcohols, dehydrogenation involves the removal of hydrogen atoms from the alcohol molecule, resulting in the formation of a double bond.

Secondary alcohols:
Secondary alcohols are alcohols in which the carbon atom carrying the hydroxyl group (OH) is bonded to two other carbon atoms. They can be represented by the general formula R2CHOH, where R represents an alkyl group.

Why dehydrogenation of secondary alcohols cannot produce aldehydes:
Aldehydes are organic compounds in which a carbonyl group (C=O) is bonded to at least one hydrogen atom. They have the general formula RCHO, where R represents an alkyl group.

When a secondary alcohol undergoes dehydrogenation, the removal of hydrogen atoms occurs from the carbon atom carrying the hydroxyl group. As a result, a double bond is formed between the carbon atom and one of the adjacent carbon atoms. However, since secondary alcohols have two alkyl groups attached to the carbon atom carrying the hydroxyl group, there is no hydrogen atom bonded directly to the carbonyl carbon. Therefore, the dehydrogenation of secondary alcohols cannot produce aldehydes.

Examples:
Let's consider an example to illustrate this:

Secondary alcohol: 2-propanol (CH3CHOHCH3)

Dehydrogenation of 2-propanol would result in the formation of a double bond between the carbon atom carrying the hydroxyl group and one of the adjacent carbon atoms. However, there are no hydrogen atoms bonded directly to the carbonyl carbon, so an aldehyde cannot be formed through this process.

In contrast, the oxidation of primary alcohols can produce aldehydes. Oxidation involves the loss of electrons and usually occurs in the presence of an oxidizing agent. Primary alcohols have a hydrogen atom bonded directly to the carbon atom carrying the hydroxyl group, allowing the formation of an aldehyde upon oxidation.

Similarly, ozonolysis of alkenes and hydration of ethyne with acid can both produce aldehydes under suitable conditions.

Therefore, the correct answer is option B: Dehydrogenation of secondary alcohols.