Question

The density of a gaseous compound is 2.06 g/L at STP. What is the most likely formula of this gas?

Ionization engergy of Na: 496 kj/mol

Electron Affinity of F: 328 kJ/mol

Energy to vaporize Na: 108 kJ/mol

F2 bond energy: 160 kJ/mol

Energy Change for the reaction:

Na (s) + 1/2F2 (g) = NaF (s) ; DeltaH = -575K

Answer 1

The density of the gas is 2.06 g/L at STP

so 22.4 L gas contains 22.4*2.06 = 46.144g substance

again we know at STP 22.4 L gas contain 1 mole of that substance

So molecular weight of that substance is 46.144 g

So any gas which has molecular weight of 46.144 g , that will be the answer

One of the example is NO₂ gas

In the next question you have not specified what I have to calculate, seeing the pattern of question I assumed that most likely it is asking for the lattice energy of NaF. So I have calculated the lattice energy.