Monomer of Novolac is :

Solution

Chemistry ma’am · 3 steps

Novolac is built from phenol and formaldehyde, but the unit that actually chains up is o-hydroxymethylphenol.

1. Where it starts. Phenol reacts with formaldehyde in the presence of an acid or base catalyst. The -CH₂OH group goes onto the ring at the ortho (or para) position, giving o-hydroxymethylphenol.

   C₆H₅OH + HCHO → o-HOC₆H₄CH₂OH

2. Chain growth. Each o-hydroxymethylphenol unit reacts with the ring of the next phenol, losing water and forming a -CH₂⁻ bridge. Repeating this gives the linear condensation polymer Novolac, which is used in paints.
3. So. The repeating unit that polymerises to Novolac is o-hydroxymethylphenol, option (c).

The idea to keep. Phenol plus formaldehyde first gives o- or p-hydroxymethylphenol. That joins up into linear Novolac, and further cross-linking with more formaldehyde turns Novolac into Bakelite.

Answer from the NTA final answer key. Solution by PrepWiser.