If $$Y$$, $$K$$ and $$\eta$$ are the values of Young's modulus, bulk modulus and modulus of rigidity of any material respectively. Choose the correct relation for these parameters.

The standard relation between Young's modulus $$Y$$, bulk modulus $$K$$, and modulus of rigidity $$\eta$$ is $$Y = \frac{9K\eta}{3K + \eta}$$.

We rearrange this to express $$K$$ in terms of $$Y$$ and $$\eta$$. Cross-multiplying, we get $$Y(3K + \eta) = 9K\eta$$.

Expanding, $$3YK + Y\eta = 9K\eta$$.

Collecting terms with $$K$$, we get $$9K\eta - 3YK = Y\eta$$, so $$K(9\eta - 3Y) = Y\eta$$.

Therefore, $$K = \frac{Y\eta}{9\eta - 3Y}$$ N m$$^{-2}$$.

Hence, the correct answer is Option C.