Answer
$$1.1 \times 10^{-25} .$$
Work Step by Step
We simplify by raising each factor to the exponent and then we divide:
$$ \left(\frac{2.5 \times 10^{-4}}{7.5 \times 10^{8}}\right)^2=\frac{(2.5 \times 10^{-4})^2}{(7.5 \times 10^{8})^2}\\
=\frac{6.25 \times 10^{-8}}{56.25 \times 10^{16}}=\frac{6.25}{56.25 } \times 10^{-8-16}\\=0.11 \times 10^{-24}=1.1 \times 10^{-25} .$$
