A really hard chemistry question,smart people please help!!?

The pressure at the points at the same level of a fluid which is under no horizontal acceleration, such as here, is the same. Since the water levels are the same inside and outside the tube, hence so will be the pressures.. Neglecting the Surface Tension of water with the equipment in these cirstances( as data related to it is not given ), the vapour pressure of water inside the tube( 2.5 KPa ) + that of H2 = Atmospheric pressure outside( 99.2 KPa ).. So, once you get H2's pressure with this equation, use PV = nRT to get n, no. of its moles. Now, Mg + 2HCl --> MgCl2 + H2.. You can see the ratio of the moles of HCl used and of H2 evolved clearly with this equation