Sir, please explain it.A horizontal platform is rotating with uniform angular velocity around the vertical axis passing through its centre. At some instant of time a viscous fluid of mass 'm' is dropped at the centre and is allowed to spread out and finally fall. The angular velocity during this period:ChoicesA.decreases continuouslyB.decreases initially and increases againC.remains unalteredD.increases continuously

As there is no external torque present here,the angular momentum is conserved.

or,     Angular momentum=(moment of inertia)*(angular velocity)=constant

So,as liquid got spread out mass getting farther from center increases the overall moment of inertia.Hence the decrease inangular velocity first ,but then liquid falling through perimeter of disk again decreases the moment of inertia until it become same as before asbefore pouring of liquid.Thus the angular velocity increases for that time to be the previous value.

Therefore the decrease initially & then increase again in the value of angular velocity.