Explanation:

- 19 September 1999 was a Sunday.

- Let's count the days from 19 September 1999 to 19 January 2001.

- From 19 September 1999 to 19 September 2000 is 1 year. 2000 is a leap year, so it adds 366 days.

- From 19 September 2000 to 19 January 2001:

- 19 September to 19 October: 1 month (30 days)

- 19 October to 19 November: 1 month (31 days)

- 19 November to 19 December: 1 month (30 days)

- 19 December to 19 January: 1 month (31 days)

- Total = 30 + 31 + 30 + 31 = 122 days

- Total days = 366 (leap year) + 122 = 488 days.

- Days of week repeat every 7 days, so 488 mod 7 = 5.

- Counting 5 days from Sunday: Monday (1), Tuesday (2), Wednesday (3), Thursday (4), Friday (5).

- So, 19 January 2001 was a Friday.

Option:1- Friday (Correct)