I have a few questions from my homework and I was wondering if I can get some help

1. In the chemical reaction between aqueous magnesium chloride and sodium metal, how many mol of magnesium metal can be precipitated with 12.6 mol of sodium metal? MgCl2(aq) + 2Na(s) --> 2NaCl(aq) + Mg(s)

2. A student correctly balanced the following chemical reaction, but forgot to include states of matter. What mass of solid precipitate can be expected to form if 23.08 g of silver nitrate is reacted with excess sodium carbonate? 2AgNO3 + Na2CO3 --> 2NaNO3 + Ag2CO3

3. When ammonia decomposes, it breaks down into nitrogen gas and hyrdogen gas. What mass of ammonia is needed to produce 50.00 g of hydrogen gas?

Just a bit stuck, thanks a ton.