(18. A bead is moving on a circular wire frame of radius \( R=12 cm \) if velocity given to bead at its lowest point is \( v=\sqrt{4 g R} \) then height at which normal reaction exerted by frame on bead will be zero is :
(1) \( 8 cm \)
(2) \( 20 cm \)
(3) \( 12 cm \)
(4) \( 24 cm \)
