From the equation Pv = n RT for the two gases. We can write

0.8 x 0.5 = n_{H2 }x RT or n_{H2 } = 0.8 x 0.5 / RT

ALSO 0.7 x 2.0 = n_{02} . RT or n_{02 } = 0.7 x 2 / RT

When introduced in 1 L vessel, then

Px1L = (n_{02 }+ n_{H2}) RT

Putting the values, we get

P = 0.4 + 1.4 = 1.8 bar

Hence, the total pressure of the gaseous mixture in the vessel is 1.8 bar