The Elementary Chemical Reaction O + ClO $\to$ Cl + O₂ is Made Pseudo-First Order in Oxygen Atoms

The elementary chemical reaction O + ClO $\to$ Cl + O₂ is made pseudo-first order in oxygen atoms by using a large excess of ClO radicals.The rate constant for the reaction is 2.7 cm³/molecule.s.If the initial concentration of ClO is 1.0 $\times$ 10¹¹ molecules/cm³,how long will it take for the oxygen atoms to decrease to 10.% of their initial concentration?

A) 1.2 s
B) 0.039 s
C) 0.26 s
D) 0.85 s
E) 2.6 s