Question

When sodium reacts with excess of oxygen, the oxidation number of oxygen changes from :

• A. 0 to -1
• B. 0 to -2
• C. -1 to -2
• D. no change

Answer 1

The correct option is A 0 to -1

when sodium reacts with excess of oxygen, it lead to the formation of metal oxides such as sodium peroxide.

$2Na+{\stackrel{0}{O}}_2\to {Na}_2{\stackrel{-1}{O}}_2$

hence there is a change in oxidation state from 0 to -1.