which two formulas represents compounds? A: NaCI B: Ag C:HCI D: H2 me needs answer i need to pass this:20 points

Can someone me with 3 and 4 plz. this is for masteries test.

What mass of natural gas (ch4) must you burn to emit 276 kj of heat?

Ammonium perchlorate nh4clo4 is the solid rocket fuel used by the u.s. space shuttle. it reacts with itself to produce nitrogen gas n2 , chlorine gas cl2 , oxygen gas o2 , water h2o , and a great deal of energy. what mass of nitrogen gas is produced by the reaction of 2.1g of ammonium perchlorate?