A diatomic gas adsorbs dissociatively on a surface, so that $θ = \frac{( K p ) ^{1/2}}{1 + ( K p ) ^{1/2}}$ . At very low coverage, the pressure is increased nine-fold. The coverage then increases by a factor of approximately:

Answer: C

When coverage is very low,

(K p)^{1/2} ≪ 1

, so

θ \approx (K p)^{1/2}

and

θ \propto p^{1/2}

. A nine-fold pressure increase therefore multiplies

θ

9^{1/2} = 3

. A nine-fold increase would be the result for non-dissociative adsorption.