If polar ice caps melt, then the angular velocity of rotation of earth:

The correct option is C decreases
No external torque.
$\therefore$ Angular Momentum will remain conserved.
$\therefore L_1=L_2$
$\therefore I_1{\omega }_1=I_2{\omega }_2$
If polar ice melts, then mass will move into the oceans due the which moment of inertia $l$ will increase, which results in decrease in the angular velocity.