Explanation:

Tautomerism:
Tautomerism is a type of structural isomerism in which a compound exists in two or more forms that readily interconvert by a chemical reaction called tautomerization. These forms are known as tautomers and they differ in the position of a hydrogen atom and a double bond. The interconversion between tautomers involves the migration of a hydrogen atom and the rearrangement of bonds.

Acetaldehyde (CH3CHO):
Acetaldehyde is an organic compound with the formula CH3CHO. It contains a carbonyl group (C=O) attached to a methyl group (CH3). In acetaldehyde, the carbonyl group is located at the terminal carbon atom. It can exist in two tautomeric forms:

1. Keto Form: In the keto form, the hydrogen atom is attached to the carbon atom of the carbonyl group. This is the predominant form of acetaldehyde.

2. Enol Form: In the enol form, the hydrogen atom is attached to the adjacent carbon atom, resulting in the formation of a double bond between the two carbon atoms.

Ethanol (CH3CH2OH):
Ethanol is an organic compound with the formula CH3CH2OH. It contains a hydroxyl group (-OH) attached to a two-carbon chain. Unlike acetaldehyde, ethanol does not exhibit tautomeric forms.

Acetaldehyde and Ethanol:
Acetaldehyde and ethanol are both organic compounds with similar chemical structures. However, acetaldehyde exhibits tautomeric forms, while ethanol does not. Therefore, the correct answer is option B) tautomerism. Acetaldehyde can exist in both the keto and enol forms due to the migration of a hydrogen atom and the rearrangement of bonds. Ethanol, on the other hand, does not undergo such tautomeric interconversion.

Summary:
Acetaldehyde exhibits tautomerism as it exists in keto and enol forms, while ethanol does not exhibit tautomerism.