Which of the following quantities is dimensionless?

The dimension of $P = \frac{B^2 l^2}{m}$ is,where $B = \text{magnetic field}$,$l = \text{length}$,$m = \text{mass}$.

Two quantities $A$ and $B$ are related by the equation $A/B = m$,where $m$ is linear density and $A$ is force. The dimensions of $B$ are equivalent to which of the following?

The dimensions of power are

Find the dimensional formula of $\rho g v$,where $\rho = \text{density}$,$g = \text{acceleration}$,and $v = \text{velocity}$.

Let the inductance and resistance be denoted by $L$ and $R$ respectively. The dimensions of $\left(\frac{L}{R}\right)$ are