Why is it incorrect to say iron is heavier than wood?

It is correct to say iron is heavier than the wood.

Explanation:

It's because the density of iron is more than wood. What is this mean is iron the space between iron molecules in iron much less than as that of wood. So in iron there is more molecules than wood in same volume. More molecules means more mass, that's why iron is much heavier than wood for same volume.

the answer is b ) square root of 5