Explanation
Due to centrifugal force.
Since force is not acting on centre of mass, it will produced torque hence linear and angular acceleration both will change.
Remains conserved until the torque acting on it remain zero.
When the hands are outstretched, moment of inertia increases and angular velocity decreases so that angular momentum remains unchanged.
Melting of ice produces water will spread over larger distance away from the axis of rotation. This increases the moment of inertia so angular velocity decreases.
In this process I decreases and ω increases.
In the absence of external torque angular momentum remains constant.
He decreases his Moment of inertia by this act and therefore increases his angular velocity.
Since no external torque acts on sphere, hence its total angular momentum remains constant.
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