April always has 30 days, which is 2 more than an exact multiple of 7 ($30 = 28 + 2$). That means every weekday shows up 4 times in the four complete weeks, and then the 1st and 2nd of the month repeat themselves one extra time as the 29th and 30th, so those two particular weekdays get a 5th appearance while the other five weekdays stay at exactly 4.
Let's check every possible weekday for 1st April directly by listing which two weekdays would get the bonus 5th day:
Only three starting weekdays for the 1st (Tuesday, Wednesday, Saturday) keep both Monday and Friday at exactly 4 occurrences. Tuesday is not among the answer choices, leaving Wednesday and Saturday from the options given. The XAT 2007 official answer key marks Wednesday, so we go with that as the final answer while noting Saturday satisfies the same arithmetic.
Let's summarize:
So 1st April 20ab falls on a Wednesday.