Let's see the formula of percent yield:
[tex]\text{Percent yield=}\frac{actual\text{ yield}}{theoretical\text{ yield}}\cdot100.[/tex]Our actual yield is what we got from the reaction, which is 4.80 g and the theoretical yield is 5.30 g, so replacing these values in the formula we're going to obtain:
[tex]\begin{gathered} \text{Percent yield=}\frac{4.80g}{5.30g}\cdot100, \\ \text{Percent yield}=90.566\%. \end{gathered}[/tex]The percent yield of MgO is 90.566%.
