Explanation

He was born in December 12, 1990.

وہ 12 دسمبر 1990 کو پیدا ہوئے۔

For month, year, and season, we use in.

For month, year, and season, we use in.

For example in August, in 1992, in the '90s, in winter.

For date and day, we use on.

For example 5 of August, on the fifth, on Monday.