Question

When an alkaline earth metal, M, reacts with oxygen the formula of the compound produced will be
a. M₂O
b. MO
c. M₂O₃
d. MO₂
e. M₃O₄

Answer 1

D as the oxygen has gained to electrons from the magnesium in the reaction.

Answer 2

the answer is M2O

why?

the assumed valency of M should be 1+ ( because it reacts with oxygen and the valency is not provided)

the valency of oxygen is O2-

thus, by cris cross technique, we get M2O