The ratio of the area of a square to that of the square drawn on diagonal is :

Answer: Option C

$$\begin{array}{rl}& \text{Required ratio}\\ & =\frac{a^2}{{\left(\sqrt{2}a\right)}^2}\\ & =\frac{a^2}{2a^2}\\ & =\frac{1}{2}\\ & =1:2\end{array}$$