Question

What is the general formula for oxide of element $M$ with atomic number 87?

• A. $M_{2}O$
• B. $MO$
• C. $M_2{O}_3$
• D. $M{O}_2$

Answer 1

The correct option is A $M_{2}O$

Electronic configuration of $M$ is $[Rn{]}^{86}7s^1$. Since $M$ has one electron in outermost $s$ orbital its valency will be 1 i.e, alkali metal. Hence, the general formula of its oxide is $M_{2}O$.