Question

Fe2O3 + H2 --> Fe + H2O

Answer 1

A) 10.0g of Iron is $\frac{10.0}{55.8}=179mmol$ of Iron.

One mole of dihydrogen is required to form one mole of iron, hence you'll need $0.179*1.00=0.179g$ of dihydrogen.

B) Likewise : 2.50g of Iron is $\frac{2.50}{55.8}=44.8mmol$ of Iron, hence we'll need $44.8*(3*16+2*55.8)=7.15g$ of Fe2O3.