CBSE Class 10 Science 2017 · Paper 31/1/1/C · Question 11

(i) Electronic configuration of M: $2,8,2$. M loses its two valence electrons to attain the configuration of neon, so its valency is $2$. (ii) M is a metal. Its atom has only two electrons in its outermost shell, which it loses easily to form a positive ion, ${\text{M}}^{2+}$; losing electrons to form positive ions is characteristic of metals. (M is magnesium, in Group 2.) (iii) Formula of the oxide: MO (magnesium oxide, $\text{MgO}$). Nature: basic — it dissolves in water to form magnesium hydroxide, $\text{MgO}+{\text{H}}_2\text{O}\to {\text{Mg(OH)}}_2$, which turns red litmus blue.