Correct Answer: Monday

Solution : Code for months –

Code for days –

Code for centuries –

For, 20th of July 2009 –
Formula: {Date + (Month code) + (Century code) + ( last two digit of the year) + ((last two digit of the year / 4)'s Quotient)} / 7
Date = 20
Code for the month (July) = 6
Code for the century (2000) = 6
(2009 = 2000 + 09; For 2000 it will be 6 and for 9 it will be 9)
And, 9 ÷ 4 = 2(Quotient)
Now, on adding them we get→20 + 6 + 6 + 9 + 2 = 43
On dividing 43 by 7, we get 1 as a remainder.
1 is the code for Monday.

So, the 20th of July 2009 will be Monday. Hence, the third option is correct.