The total number of monohydric phenol of molecular formula C7H8O.A 5 B 4 C 2 D 3

The molecular formula C7H8O represents a phenol molecule with 7 carbon atoms. Monohydric phenols are phenols that have only one hydroxyl group.

Step 1: Draw the basic structure of a phenol molecule. It consists of a benzene ring (6 carbon atoms) with one hydroxyl group attached.

Step 2: Now, we have one extra carbon atom (as the molecular formula is C7H8O). This carbon atom can be attached to the benzene ring in three different ways: ortho, meta, and para positions.

Step 3: The ortho and meta positions will give us two different structures. The para position will give us the same structure as the ortho position.

Step 4: We also have the possibility of attaching the extra carbon atom to the hydroxyl group, giving us another unique structure.

So, in total, we have 3 unique structures of monohydric phenols with the molecular formula C7H8O. Therefore, the answer is D) 3.