Question

How many moles of O2 are required for the combustion of 5 moles of
Mg?

Answer 1

According to the equation

2Mg + O₂ = 2MgO

the amount of substance of oxygen will be equal to:

$\nu$ (O₂) = $1/2 • \nu(Mg)$ = 1/2 • 5(mol) = 2.5 mol

Answer: $\nu$ (O₂) = 2.5 mol