Please help me because I don't know how to calculate mol and gram

If soap hits the floor, is the soap dirty or the floor

Calculate the number of molecules present in 0.750 mol of mgo.

3. how much energy in joules is required to evaporate .0005 kg of liquid ammonia to vapor at the same temperature? 4. how much energy ( in megajoules ) is given up by .75 kg of water at 0c when it freezes to form ice at 0c? 5. explain how heat works between and at critical temperatures?