Identify the part of speech of the highlighted word in the sentence given below.
It shall be done by then.

Correct option is D

Correct answer: (d) Adverb
Explanation (highlight):
• Then tells time (by what time).
• Words that tell time/place/manner of an action are adverbs.
Example: Finish the work by then.
Why other options are incorrect:
• (a) Noun → not a name of a person/place/thing here.
• (b) Pronoun → does not replace a noun.
• (c) Adjective → does not describe a noun.
Hence, option (d) is the correct answer.