Question

one must finish his duty on time.spot the error​

Answer 1

Answer:

his - own or one's........

Answer 2

Answer:

One must finish their duty on time.

Explanation:

The word his used in the given sentence was erroneous and their will be used in its place. The pronoun his is a personal third person pronoun and usually indicates possession. For example: It was his book. Here the book belongs to him and to show the sense of belongingness his has been used. His is also used to refer to the male gender.  

However one is a universal pronoun and implies no gender. One also has a sense of plurality where as his is always singular. Therefore there is used in the place of his as it is grammatically correct.