To find we need to begin by finding the gram formula mass of the ##Mg(NO_3)_2## compound.

Mg 1 atom x 24.31 = 24.31 N 2 atoms x 14.01 = 28.02 O 6 atoms x 15.99 = 95.94 Total Mass = 148.27 g/mol

% Magnesium = ##(24.31/148.27)##= .164 or 16.4 % % Nitrogen = ##(28.02/148.27)## = .189 or 18.9% % Oxygen = ##(95.94/148.27)## = .647 or 64.7%

I hope this was beneficial. SMARTERTEACHER