When a gas is compressed in a cylinder the amount (mass) of gas
a.

increases
b.

decreases
c.

increases initially then decreases
d.

remains unchanged

I believe the correct answer from the choices listed above is option D. When a gas is compressed in a cylinder the amount (mass) of gas remains unchanged. This is due to the law of conservation mass where mass cannot be created nor destroyed. In this case, it is the volume of the gas is changed not the mass.

You know how the first one if filled up like the objects do the same but with the other categories