Identify the reagent used in Reimer-Tiemann reaction,

The Reimer-Tiemann reaction involves the treatment of phenol with chloroform ($\text{CHCl}_3$) in the presence of an aqueous base such as sodium hydroxide (aq. NaOH) to introduce an aldehyde group ($\text{-CHO}$) at the ortho position of the benzene ring, forming salicylaldehyde.

The electrophile generated in this reaction is dichlorocarbene ($:\text{CCl}_2$).

Therefore, the reagents used are $\text{CHCl}_3$ and aq. NaOH.

Answer: $\text{CHCl}_3$, aq.NaOH