Which of the following quantities is dimensionless?

Which one of the following is a dimensionless physical quantity?

Of the following,the pair of physical quantities not having the same dimensional formula is

The position of a particle at time $t$ is given by the equation $x(t) = \frac{v_0}{A}(1 - e^{-At})$, where $v_0$ is a constant and $A > 0$. The dimensions of $v_0$ and $A$ respectively are:

The dimensions of surface tension are

Dimensions of luminous flux are