Solid Angle

Q. The unit of solid angle is steradian. What is the dimensional formula for steradian?

1. $\left[L^1{M}^1{T}^{-1}\right]$
2. $\left[L^0{M}^0{T}^0\right]$
3. $\left[L^2{M}^{-1}{T}^1\right]$
4. $\left[L^{-2}{M}^1{T}^0\right]$

Q. Find the solid angle of a spherical surface of area $1.5\pi r^2$ at its center.

1. $1.5\pi sr$
2. $0.5\pi sr$
3. $2\pi sr$
4. $0.75\pi sr$