Q abt 鎂離子

MgCl2 is 95.2g/mol
H2O is 18g/mol
so there is 0.1 mol of Mg 2+, 0.2 mol of Cl- and 5 mol of H2O
ratio of Mg2+, Cl-, H2O is 0.1 : 0.2 : 5
or 1 : 2 : 50

12.4克Na2x中含有鈉离子0.4mol,則Na2X中的摩 質量是0.2mol,
molar mass for Na2X is 62
as the molar mass of Na is 22.9898 (23)
X的相對原子質量是16
X is O (oxygen)
Na2X is Na2O
I hope this can help your understanding. =)

molar mass for Mg is 24.312g (24)

鎂的molar mass是24g