'At the surface of a charged conductor,the electrostatic field must be normal to the surface at every point'. Explain.

If the electric field $\vec{E}$ were not normal to the surface,it would have a non-zero tangential component along the surface.
This tangential component would exert a force on the free charges present on the conductor's surface,causing them to move.
Since the conductor is in an electrostatic (stable) state,there can be no net motion of charges.
Therefore,the tangential component of the electric field must be zero.
Thus,the electrostatic field at the surface of a charged conductor must be normal to the surface at every point,given by $\vec{E} = \frac{\sigma}{\epsilon_{0}} \hat{n}$,where $\sigma$ is the surface charge density and $\hat{n}$ is the unit normal vector.