Please help!

Consider the reaction of hydrogen and oxygen to form water as follows:

2 H2 (g) + O2 (g) --> 2 H2O (l)

if 10.5 g of hydrogen are placed in a reaction vessel, how many grams of oxygen are required to fully react with the hydrogen to make water? Numerical answers only; do not include units in your answer!

Which theory was contradicted by experiments with the photoelectric effect? light spreads out after it passes through a small opening. as soon as light strikes metal, electrons will be ejected. visible light, regardless of color, will cause the ejection of electrons when striking metal. the kinetic energy of ejected electrons depends on the frequency of light that strikes the metal.