Which of the following enzymes is used to break down plant cell walls?

The correct answer is Option (2) → Cellulase

To isolate DNA, the cell has to be broken open first. The enzyme used depends on what the cell wall is made of. Plant cell walls are made mainly of cellulose, so cellulase is used for plant cells. For bacterial cells the book names lysozyme, and for fungi chitinase. Ribonuclease and protease are used later, to remove RNA and proteins from the released DNA; they do not open the cell.

NCERT Extract:
Isolation of the Genetic Material (DNA) – “… Since the DNA is enclosed within the membranes, we have to break the cell open to release DNA along with other macromolecules such as RNA, proteins, polysaccharides and also lipids. This can be achieved by treating the bacterial cells/plant or animal tissue with enzymes such as lysozyme (bacteria), cellulase (plant cells), chitinase (fungus). … The RNA can be removed by treatment with ribonuclease whereas proteins can be removed by treatment with protease.”