# Assertion (A) : In the formation of oxide ion, $O^{2-}(g)$ , first an exothermic reaction and then an endothermic reaction takes place. Reasons (R) : $O^-$ ion has comparatively large size than oxygen atom.

(1) (A) is not true but, (R) is true.

(2) (A) is true, but (R) is not true

(3) Both (A) and (R) are true, but (R) is not the correct explanation of (A)

(4) Both (A) and (R) are true,  (R) is the correct explanation of (A)

(3) Both (A) and (R) are true, but (R) is not the correct explanation of (A)