Three closed vessels A, B and C are at the same temperature. Vessel A contains only  O₂, B only N₂  and C a mixture of equal quantities of O₂ and N₂. If the average speed of  O₂ molecule in vessel A is v₁, that of  N₂ molecules in vessel B is  v₂, the average speed of  O₂ molecules in vessel C is 

• A

  $\frac{1}{2}(v_1+v_2)$

• B

  ${\text{v}}_1$

• C

  $\sqrt{v_1{v}_2}$

• D

  $\sqrt{\frac{3kT}{M}}$