Three closed vessels A, B and C are at the same temperature T and contain gases which obey the Maxwellian distribution of velocities. Vessel A contain only\[{{O}_{2}}\], B only \[{{N}_{2}}\] and C a mixture of equal quantities of \[{{O}_{2}}\] and \[{{N}_{2}}\]. If the average speed of the \[{{O}_{2}}\] molecules in vessel A is that of the \[{{N}_{2}}\] molecules in vessel B is \[{{v}_{2}},\] the average speed of the \[{{O}_{2}}\] molecules in vessel C is

• A. \[\frac{{{v}_{1}}+{{v}_{2}}}{2}\]      
• B.        \[{{v}_{1}}\]
• C. \[{{\left( {{v}_{1}}.{{v}_{2}} \right)}^{\frac{1}{2}}}\]            
• D.        \[\sqrt{\frac{3kT}{M}}\]