What mass of magnesium oxide is produced from 2.00 moles of magnesium?

Looks like stoichiometry.

Magnesium oxide = MgO
Gotta know the equation for how it is formed: Mg + O2 ⇒ MgO

Then you have to balance the equation. 2Mg + O2 ⇒ 2MgO

Look on the periodic table to find molar mass of Mg and O
Mm Mg = 24.31
Mm O = 15.999

The equation shows you have 2 mol Mg makes 2 mol MgO

So molar mass of 1 mole MgO = 24.31+15.999 = 40.309

We need 2 moles of MgO because we had 2 mol Mg so
2 mol MgO x 40.309 g = 80.6 g

The answer is 1.82 j/g°c                  

B. nuclear reactions could first occur.