Friction is the force you get when you (for example) Rub something with another, it's a force that may generate heat and even some resistance. Another example is rubbing your hands together, they get hot, therefore friction is working, without friction you wouldn't be able to stop moving.
Our data are,
State 1:

State 2:

We know as well that 
To find the mass we apply the ideal gas formula, which is given by

Re-arrange for m,

Because of the pressure, temperature and volume ratio of state 1 and 2, we have to

Replacing,

For conservative energy we have, (Cv = 0.718)

D...because most of the mass of an atom comes from the nucleus so its not true so D is the correct answer