On the 6 March, 2005, Monday falls. What was the day of the week on 7th March 2004?

6th March 2005 = Monday.
Then, 6th March 2004 = Monday - 1 day = Sunday
[ ∵ 2004 is a leap year but it does not cross 29th February of 2004, so only 1 is taken as odd day. ]
6th March 2004 = Sunday
7th march 2004 = Monday.