$4:15$

$4:25$

$3:15$

$3:25$

B. $4:25$

Let the diagonals of the squares be 2x and 5x.

Then ratio of their areas will be

$Areaofsquare=\frac{1}{2}*Diagona{l}^{2}\phantom{\rule{0ex}{0ex}}\frac{1}{2}*2{x}^{2}:\frac{1}{2}*5{x}^{2}\phantom{\rule{0ex}{0ex}}4{x}^{2}:25{x}^{2}=4:25$