Answer:
Angular momentum, 
Explanation:
It is given that,
Radius of the axle, 
Tension acting on the top, T = 3.15 N
Time taken by the string to unwind, t = 0.32 s
We know that the rate of change of angular momentum is equal to the torque acting on the torque. The relation is given by :

Torque acting on the top is given by :

Here, F is the tension acting on it. Torque acting on the top is given by :





So, the angular momentum acquired by the top is
. Hence, this is the required solution.
Mechanical energy is the answer
Decreases density because gases have less density than liquids
There's actually potential energy before the kinetic energy came into play, but the sum of potential and kinetic energy is MECHANICAL ENERGY.