For which of the following reactions is the degree of dissociation (α) and equilibrium constant (Kp) related as Kp = 4α² / (1) α²)?

(a) N₂(g) ⇌ 2N(g)
(b) H₂(g) ⇌ 2H(g)
(c) CO(g) ⇌ C(g) + O(g)
(d) Cl₂(g) ⇌ 2Cl(g)