While painting new wood work, the process of filling up of nail holes, dents, and cracks with putty is known as ______.

Correct option is C

Stopping is the process of filling nail holes, dents, and small cracks in new woodwork with putty before painting.

Also,

Caulking → sealing joints/gaps

Blocking → not related to putty filling

Knotting → treating resinous knots in timber