A unitless quantity?

Dimension of $\frac{1}{\mu_0 \varepsilon_0}$ should be equal to

Given below are two statements: One is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$ : Product of Pressure $(P)$ and time $(t)$ has the same dimension as that of coefficient of viscosity.
Reason $R$ : Coefficient of viscosity $=\frac{\text { Force }}{\text { Velocity gradient }}$
Question : Choose the correct answer from the options given below 

If the dimensions of a physical quantity are given by $M^aL^bT^c$ ,then physical quantity will be 

The dimensions of electric potential are

The dimensional formula for the modulus of rigidity is