Question

the portion of a nail which is actively growing is the nail matrix. nail body. lunula. nail root.

Explanation:

The nail matrix is the actively - growing part of the nail. It is where new nail cells are produced, pushing the older cells forward to form the nail plate. The nail body is the visible part of the nail, the lunula is the crescent - shaped white area at the base of the nail, and the nail root is the part hidden under the skin at the base of the nail.

Answer:

nail matrix.