Answer
See answer below.
Work Step by Step
a) From the standard states:
$Mg(s)+1/2\ O_2(g)\rightarrow MgO(s)$
Enthalpy of formation:
$-601.24\ kJ/mol$
b) Enthalpy:
$-601.24\ kJ/mol\times 2.5\ mol = -1503.1\ kJ/mol$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.