How many moles of H2O will be produced if 6.8 mol of O2 reacts with CH4?

How much would the freezing point of water decrease if 4 mol of nacl were added to 1 kg of water (kf=1.86 degrees c/(mol/kg) for water and i=2 for nacl a- 7.44 degrees c b- 14.88 c 3.72 d 1.86