The electrical resistance $$R$$ of a conductor of length $$l$$ and area of cross section $$a$$ is given by $$R = \frac{\rho l}{a}$$ where '$$\rho$$' is the electrical resistivity. What is the dimensional formula for electrical conductivity '$$\sigma$$' which is reciprocal of resistivity?

A

$$[M^{-1} L^{-3} T^3 A^2]$$

B

$$[M L^{-3} T^{-3} A^2]$$

C

$$[M L^3 T^{-3} A^{-2}]$$

D

$$[M^{-2} L^3 T^2 A^{-1}]$$