Q.State the formula for angle of banking.

The banking angle formula relates the safe speed, radius of the curve and acceleration due to gravity.

For a vehicle moving on a banked circular road (without friction) with banking angle $\theta$, radius $r$, at speed $v$, the horizontal component of the normal reaction supplies the required centripetal force …

Friction is what supplies centripetal force on a flat curve; banking removes that need.

On a level (unbanked) road, the only horizontal force available to turn a vehicle is friction between tyres and road — with friction reduced to zero, no centripetal force is available and the vehicle cannot negotiate any curve; it would skid straight off the road.

On a banked road, however, the horizontal component of the normal reaction itself can supply the centripetal force, without any help from friction, provided the vehicle travels at exactly the speed the banking was designed for:

$v = \sqrt{rg\tan\theta}$ …