The density of an unknown gas at STP is 1.63 g/L. Is the gas H2(g), N2(g), HCl(g), or CO2(g)

Most likely a is the answer - because  you generate   38 atp's but also consume an atp.   each atp gives approx. less than 4 kcal so probably a is the closest answer.

Ithink this is what you meant. the temperature at which a liquid begins to boil is called the boiling point. the boiling point of water is 212°f or 100°c.  and at that point will start to turn into steam (gas)

Must be negative.substance increases