I got it right (guessed that it would sort alphabetically to remove duplicates, but that's not guaranteed, as mentioned)

However, I reckon that *none* of the answers are (or should that be 'is?) correct.

I would prefer to see

NULL, '1' and NULL,'manoj' (2 rows)

rather than

NULL, 1 and NULL,'manoj' (2 rows)

as the answer, as all the second-field values are clearly stated as character strings.

Some may call that being picky, but hey, two of the 'mutually exclusive' answers are actually the same, according to set theory.