Every perfect square which is an odd number can be represented as the difference of two consecutive perfect squares. The odd numbers less than 100 (which is the square root of 10000) should be the answer. So, the answer is 50

Explanation:

Consider (x+1)^2 and x^2 be two consecutive perfect squares.

Difference of those two:

(x+1)^2 - x^2

= x^2 + 2x + 1 - x^2

= 2x + 1 = is an odd number and should also be a perfect square.

For example: consider an odd perfect square : 25

Which can be written as 2(12)+1here, x=12

25 can be written as (x+1)^2 - x^2

= (12+1)^2 - 12^2

= 13^2 - 12^2

= 169 - 144

= 25

I hope you understood.