Bakelite is obtained from phenol by reacting it with

Bakelite is a thermosetting polymer made in two main steps.

Step 1 - Formation of the linear (novolac) polymer: Phenol first reacts with formaldehyde, $$HCHO$$, in the presence of a little acid or base to give a linear product called novolac. The -CH2- bridges join the ortho and para positions of different phenol rings.

Step 2 - Cross-linking to Bakelite: On further heating with more formaldehyde and a catalyst such as hexamethylenetetramine, extensive -CH2- cross-links are formed. The three-dimensional, rigid, infusible network so produced is called Bakelite.

Because formaldehyde is the essential reagent that links phenol units together, only Option C fits.

Option C which is: Formaldehyde