In order to find the difference of two squares, each term needs to be a perfect square.
Since each variable is multiplied by a constant, both the constant and the variable needs to be a perfect square.
In order for the variable to be a perfect square, its exponent needs to be even.
In the first option, the exponents are odd.
In the third option, the number 12 is not a perfect square.
In the fourth option, we have a sum instead of a difference.
In the second option, we have:
[tex]\begin{gathered} 25a^2-36b^2 \\ =(5a)^2-(6b)^2 \end{gathered}[/tex]
Therefore the correct option is the second one.
