How many moles of oxygen gas are required to react with 2.0 moles of sugar?

Stoichiometry comes down to the mole ratios, as given by the balanced chemical equation. Your balanced equation says that 1 mole of sugar will react with 12 moles of oxygen to make 12 moles of CO2 and 11 moles of water. If 12 moles of oxygen reacts with 1 mole sugar, then how many moles of oxygen will react with 2 moles of sugar? Despite the fact that sugar can be used for model rocket fuel, this ain't rocket science.

As for the other two, you still have to work with the mole ratios as given by the balanced equation. But you have to covert the mass of NH3 to moles first, then figure out the moles of ammonium chloride and then convert it back to grams. This is best done with a couple of conversion factors.

Density and pressure