Correct option is: C) 25 cm
We have l = 9 cm, b = 12 cm & h = 20 cm.
\(\therefore\) The length of the diagonal of cuboid = \(\sqrt {l^2 + b^2 + h^2}\)
= \(\sqrt {9^2 + 12^2 + 20^2} = \sqrt {81 + 144 + 400} = \sqrt {625} = 25 cm\)
Hence, the diagonal of the cuboid is 25 cm.
