2021/003) Which of the following numbers is a perfect square? (A) 98! · 99! (B) 98! · 100! (C) 99! · 100! (D) 99! · 101! (E) 100! · 101!

The above are of the form $(n!)^2 * (n+1)$ or  $(n!)^2 * (n+1)(n+2)$

so we need to check if (n+1) or (n+1)(n+2) is a perfect square and based ion that n = 100 is a perfect square. So ans is (C).