In the reaction h2 + n2 2 nh3, what coefficient should be placed in front of h2 to balance the reaction

Iknow the answer is a but i don't know why

If the particles in a sample of matter have an orderly arrangement and move only in place, the sample is a

Write the empirical chemical formula of calcium with a mass percent of 38.8, phosphorus with a mass percent of 20.0, and oxygen with a mass percent of 41.3.