The answer is [Boron]
I had this answer on my Chemistry test!
We subtract the enthalpies of the reactants from that of the products:

Since this is < 0, this is an exothermic reaction.
The electron, due to the way an electron orbits the nucleus of an atom.
According to Quantum Mechanics, electrons do not really orbit the nucleus of an atom. In fact, the most tightly bound state, the 1s orbital, has no angular momentum at all. This would be the state with the most "kinetic energy" and yet there is no "orbital" motion at all in this state.
We assume that this gas is an ideal gas. We use the ideal gas equation to calculate the amount of the gas in moles. It is expressed as:
PV = nRT
(672) (1/760) (36.52) = n (0.08206) ( 68 +273.15)
n = 1.15 mol of gas
Hope this answers the question. Have a nice day.