Question

Find the oxidation number of Calcium in $CaO$.

• A. 1
• B. -1
• C. 2
• D. -2

Answer 1

The correct option is C 2

Calcium has $20$ electrons, and its electronic configuration can be written as $2,8,8,2$. Thus, Calcium has $2$ electrons in its outermost orbit or it can be said that Calcium has $2$ valence electrons. $Ca$ wants to give away these two valence electrons to its neighboring Oxygen atom in $CaO$. Calcium thus completes its octet by giving away the two valence electrons and attains the electronic configuration of its nearest inert gas Argon. Thus, Calcium now has $18$ electrons and hence its oxidation number becomes $+2$.