If 20 March 2001 is Tuesday, then what will be the day of the week on 23 April 2021 ?

Correct option is A

An ordinary year has 1 odd day and a leap year has 2 odd days. 
If 20 March 2001 is Tuesday, 
20 March 2002 – Wednesday
20 March 2003 – Thursday
20 March 2004 – Saturday (Leap year)
20 March 2005 – Sunday
20 March 2006 – Monday
20 March 2007 – Tuesday
20 March 2008 – Thursday (leap year)
20 March 2009 – Friday
20 March 2010 – Saturday
20 March 2011 – Sunday
20 March 2012 – Tuesday (Leap year)
20 March 2013 – Wednesday
20 March 2014 – Thursday
20 March 2015 – Friday
20 March 2016 – Sunday (Leap year)
20 March 2017 – Monday
20 March 2018 – Tuesday
20 March 2019 – Wednesday
20 March 2020 – Friday (Leap year)
20 March 2021 – Saturday
Number of days between 20 March 2021 to 23 April 2021 = (11 + 23) = 34
34 when divided by 7, leaves 6 as remainder.
Saturday + 6 = Friday
Therefore, it will be Friday on 23 April 2021.