The molar mass of the M2O = 2(molar mass of M) + molar mass of oxygen
Molar mass of oxygen = 16
Therefore:
231.74 = 2(molar mass of M) + 16
215.74 = 2*molar mass of M
molar mass of M = 107.87 grams
Now, from the given formula, we can notice that the metal M is monovalnet and we know that chlorine is monovalent as well.
Therefore, the compound formed will be: MCl
molar mass of chlorine = 35.5 grams
Therefore,
molar mass of MCl = 107.87 + 35.5 = 143.37 grams