Poly substitution is a major drawback in
(a)Reimer Tiemann reaction
(b)Friedel Crafts acylation
(c)Friedel Crafts alkylation
(d)acetylation of aniline.

Options

A. Reimer Tiemann reaction
B. Friedel Crafts acylation
C. Friedel Crafts alkylation
D. acetylation of aniline.

Answer

To solve the question regarding poly substitution being a major drawback in certain reactions, we can analyze each option provided:

### Step 1: Understand the Reactions
1. **Reimer-Tiemann Reaction**: This reaction involves the ortho-formylation of phenols and does not typically lead to poly substitution.
2. **Friedel-Crafts Acylation**: This reaction introduces an acyl group to an aromatic ring and generally does not lead to poly substitution due to the stability of the acylated product.
3. **Friedel-Crafts Alkylation**: This reaction introduces an alkyl group to an aromatic ring. The product formed is highly reactive and can lead to multiple substitutions on the aromatic ring, resulting in poly substitution.
4. **Acetylation of Aniline**: This reaction involves the introduction of an acetyl group to an aniline compound and does not lead to poly substitution due to the less reactive nature of the product.

### Step 2: Identify the Major Drawback
From the analysis:
- The Friedel-Crafts alkylation is known for poly substitution because the alkyl groups are activating and can lead to further substitutions on the aromatic ring.

### Conclusion
The correct answer to the question is:
**(c) Friedel Crafts alkylation**