Step 1: Recognizing the reaction type.
Phenol (here 4-methyl phenol) reacts with chloroform in presence of NaOH via Reimer–Tiemann reaction, which introduces a formyl group (\(-CHO\)) at ortho and para positions.
Step 2: Activation of phenoxide ion.
NaOH converts phenol into phenoxide ion, which strongly activates the benzene ring toward electrophilic substitution, especially at ortho and para positions.
Step 3: Role of chloroform.
CHCl\(_3\) generates dichlorocarbene (:CCl\(_2\)) in basic medium, which acts as the electrophile in the reaction.
Step 4: Orientation effect of substituents.
In 4-methyl phenol, both OH and CH\(_3\) are ortho/para directing groups. However, steric hindrance favors substitution at the para position relative to OH group.
Step 5: Product formation.
Thus, formyl group enters mainly at the para position forming p-hydroxybenzaldehyde derivative.
Step 6: Final conclusion.
Hence, the major product is para-substituted aldehyde derivative.
Final Answer:
\[
\boxed{\text{p-hydroxybenzaldehyde derivative}}
\]