Correct Answer: Sunday

Solution : Given:
11 October 1965 is a Monday.

Let's calculate the total number of days from the 11th of October 1965 to the 15th of July 1973 –

Number of days from 11 October 1965 to 31 December 1965 = 20 + 30 + 31 = 81
Number of days from 1 January 1966 to 31 December 1972 = (7 × 365) + 2 = 2557 (2 leap years)
Number of days from 1 January 1973 to 15 July 1973 = 31 + 28 + 31 + 30 + 31 + 30 + 15 = 196
So, the total number of days from 11 October 1965 to 15 July 1973 = 81 + 2557 + 196 = 2834
Now, on dividing 2834 by 7, we get 404 as the quotient and 6 as the remainder.

Therefore, add 6 to Monday, Monday + 6 = Sunday

So, the 15th of July 1973 will be Sunday. Hence, the fourth option is correct.