They both depend upon each other the bigger one is the smaller the other can be.
A) 10.0g of Iron is

of Iron.
One mole of dihydrogen is required to form one mole of iron, hence you'll need

of dihydrogen.
B) Likewise : 2.50g of Iron is

of Iron, hence we'll need

of Fe2O3.
(1.632) (4.0 x 104)
= (1.632)(416)
=678.912
6.8* 10^2.
Not sure if it's the right sig figs.
Because of the plates crashing into each other