Answer
Mg has atomic number 12; hence, it has 12 protons. Isotopes of Mg are:
Mass No. 12 + 12 = 24 : $^{24}_{12}Mg$
Mass No. 12 + 13 = 25 : $^{25}_{12}Mg$
Mass No. 12 + 14 = 26 : $^{26}_{12}Mg$
Work Step by Step
Mg has atomic number 12; hence, it has 12 protons. Isotopes of Mg are:
Mass No. 12 + 12 = 24 : $^{24}_{12}Mg$
Mass No. 12 + 13 = 25 : $^{25}_{12}Mg$
Mass No. 12 + 14 = 26 : $^{26}_{12}Mg$