Which option gives a correct reason for ligase reaction failure?

Correct answer: The ligase enzyme is inactive

Successful ligation requires an active ligase, suitable DNA ends, an appropriate reaction buffer, and the chemical energy needed to activate the DNA ends. If the enzyme has lost its activity because of improper storage, excessive heat, unsuitable pH, or another damaging condition, it cannot catalyse phosphodiester-bond formation even when the DNA fragments are compatible. Thus option A is the correct reason for reaction failure. Compatible ends in B generally promote joining, while a proper buffer in C supports enzyme function. The availability of ATP or another required cofactor in D supports ligation rather than causing failure.