Question

How much oxygen is required for the complete combustion of 220 g of propane is

Answer 1

combustion means any chemical compound burns in the present of air { e.g., oxygen }
you should noticed that if any hydrocarbon is burned in the present of air/oxygen then in place of products carbon dioxide and water form.
chemical formula of propane is $C_3H_8$.
see the combustion reaction :
$C_3H_8+5O_2\rightarrow 3CO_2+4H_2O$

here you can see for combustion of 1 mole of propane , required 5 mole of oxygen.

now first of all, we have to find number of mole of propane in 220g
molecular weight of propane = 44 g/mol
so, mole = given weight/molecular weight
= 220/44 = 5 mol

hence, for combustion of 5 mole of propane, required 5 × 5 = 25 mole of oxygen gas.

weight of 25 mole of oxygen = 25 × 32 = 800g