I am sorry tejal but i am out of time so i cannot give you the exact answer but can tell you how to solve it.

 

 

We know that :      C_P - C_V = R     ------------------   Eq.1

And it is given that,        R / C_V = 0.67    -------------    Eq. 2

 

By using both equations you can calculate values of  C_P and C_V  .

 

Now we also know,    C_P / C_V = K     { Here K represents gamma, i.e degree of

                                                         freedom of a gas. }

 

So, valu of K will tell you whether it is monoatomic or diatomic gas or else.

 

Forum experts please check, i may be wrong.