1) the element symbol, and thus name. For example, H is hydrogen, C is carbon and Fe is iron.
2) The atomic number, which is equal to the number of protons in the nucleus.
3) Since each proton has a +1 charge, you can also figure out the number of -1 electrons in the neutral atom.
4) The atomic mass, in atomic mass units, which is an average of 1 or more isotopes of the element.
According to the periodic table, carbon's molar mass is 12.011 grams per mole (that's the small number under the element). So, just multiply like this to get the answer:

So, there are approximately 0.208 grams in 2.5 moles of carbon.
Given question is incomplete. The complete question is as follows.
Pentaborane (
) is a colorless highly reactive liquid that will burst into flames when exposed to oxygen.the reaction is:
Calculate the kilojoules of heat released per gram of the compound reacted with oxygen.the standard enthalpy of formation
,
, and
are 73.2, -1271.94, and -285.83 kJ/mol, respectively.
Explanation:
As the given reaction is as follows.
Therefore, formula to calculate the heat energy released is as follows.

Hence, putting the given values into the above formula is as follows.

= 
= -9078.59 kJ/mol
Since, 2 moles of Pentaborane reacts with oxygen. Therefore, heat of reaction for 2 moles of Pentaborane is calculated as follows.
= -71.915 kJ/g
Thus, we can conclude that heat released per gram of the compound reacted with oxygen is 71.915 kJ/g.