Answer is: Allena is correct. It is an element because it is only made of chlorine atoms.
A chemical element bonded to an identical chemical element is not a chemical compound since it is made from only one element and not from two different elements. Chlorine is molecule, but not compound.
The first one because some people might not believe that and others might believe that.
Explanation:
It is the heat required to change a gram of substance from a liquid to a gas.
There are 137 atoms in this molecule. C55 + H72 = 127. 127 + Mg (one atom of magnesium = 128. 128 + N4 = 132. 132 + O5 = 137.