$\left[ML^2 T^{-2} K^{-1}\right]$ is the dimensional formula of which physical quantity?

$MLT^{-1}$ represents the dimensional formula of

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 the reciprocal of resistivity?

$A$ function $f(\theta)$ is defined as $f(\theta) = 1 - \theta + \frac{\theta^2}{2!} - \frac{\theta^3}{3!} + \frac{\theta^4}{4!} - \dots$. Why is it necessary for $f(\theta)$ to be a dimensionless quantity?

Which of the following physical quantities has a unit but no dimensions?

Write the definition and dimensional formula of frequency.