Assertion (A): 'actus reus' is an act which is bad or prohibited, blameworthy or culpable
Reasoning (R): There are certain situations when the act in itself may appear to be a criminal act, yet it cannot be termed as actus reus.

Both A and R are correct and R is not the correct explanation of A.

‘actus reus’ in common parlance means a 'guilty act'. It is made up of three constituent parts, namely 1. An action or a conduct
2. The result of that action or conduct
3. Such act/conduct being prohibited by law
Therefore, one can say that actus reus is an act which is bad or prohibited, blameworthy or culpable. Now, there are certain unique situations when the act in itself may appear to be a criminal act, yet it cannot be termed as actus reus .An executioner's job is to hang (no actus reus) An army man kills as a part of his duty (no actus reus)