A mixture of hydrogen and oxygen contains 40 % hydrogen by mass...

According to Dalton's law of partial pressures, the total pressure by a mixture of gases is equal to the sum of the partial pressures of each of the constituent gases.

${P}_{i} = {x}_{i}P{P}_{i} = partialpressureof{i}^{th}component . {x}_{i} = molefractionofthe{i}^{th}componentP = totalpressure$

Let ${W}_{{H}_{2}} = 40g ⇒ {n}_{{H}_{2}} = \dfrac{40}{2} = 20$

${W}_{{O}_{2}} = 60g ⇒ {n}_{{O}_{2}} = \dfrac{60}{32} = \dfrac{15}{8}$

${P}_{{H}_{2}} = \left(\dfrac{20}{20 + \dfrac{15}{8}}\right) \times 2 . 2$

$= \dfrac{20}{20 + 1 . 875} \times 2 . 2$

$= \dfrac{20}{21 . 875} \times 2 . 2$

$= 2 . 0114$

$≃ 2 . 01bar$