What is the mole fraction of the solute in a 1.00 m aqueous solution?

If Avogadro number N_A, is changed from 6.022 $$ \times $$ 10²³ mol^$$-$$1 to 6.022 $$ \times $$ 10²⁰ mol^$$-$$1, this would change

A mixture of gases contains H₂ and O₂ gases in the ratio of 1 : 4 (w/w). What is the molar ratio of the two gases in the mixture ?

1.0 g of magnesium is burnt with 0.56 g O₂ in a closed vessel, Which reactant is left in excess and how much ? (At. wt. Mg = 24, O = 16)