The question consists of a problem question followed by two statements I and…

Concept: In Data Sufficiency questions, a statement (or combination of statements) is ‘sufficient’ only if it leads to one, and exactly one, definite value/answer to the question asked. If a statement or the combination of statements still leaves more than one possible answer consistent with the given conditions, the data is insufficient.

Application: Statement I confines the birthday to the days after 19th and before 25th September — that is 20th, 21st, 22nd, 23rd, and 24th September, five possible dates — so Statement I alone cannot fix a single day. Statement II states only that the birth year is a leap year; a leap year affects only February's day count (29 instead of 28) and has no bearing on how many days September has (always 30) or on which of the five candidate dates in September is the actual birthday, so Statement II alone gives no date information at all. Combining both: even after fixing the year type via Statement II, the birthday could still be any of the five days (20–24 September) identified by Statement I — the leap-year fact eliminates none of them.

Cross-check: Nothing in either statement, singly or jointly, distinguishes 20th September from 21st, 22nd, 23rd, or 24th September. Since more than one date remains fully consistent with all the given information, no single birthday can be pinned down.

Result: The information in both statements together is still not sufficient to determine Mohit's exact birthday.