Question

Arun was asked by his mother to explain the missing buttons on his shirt (use: explanation)

Answer 1

Arun was asked by his mother for an explanation of missing button on his shirt

Answer 2

If we write the sentence with the word “explanation,” we have to write it as “Arun's mother asked for an explanation about the buttons on his shirt.”

Here the word “explanation” is a noun, and it should be written in the proper place to construct a meaningful sentence.

The rewritten sentence is directly aimed at  Arun, and there is no need for “who his mother asked for.”