If the 4-digit number 4XY2 is divisible by 3, then the sum of its digits will be divisible by 3.
4 + X + Y + 2 = 6 + X + Y
6 is divisible by 3 already.
So, to make 6 + X + Y divisible by 3, X + Y should also be divisible by 3.
So the least value X + Y can take is 3.
Hence option ‘a’ is the answer.