Is work (w) being done on the gas or by the gas in the cylinder? Will the sign of work be >0 or <0?

Question

Consider a gas enclosed in a cylinder with a piston. If the gas is compressed by lowering the piston, is work (w) being done on the gas or by the gas in the cylinder? Will the sign of work be >0 or <0?

a. work done on the gas, w>0

b. work done on the gas, w<0

c. work done by the gas, w<0

d. work done by the gas, w>0

Had a lot of trouble with this question.

Answer 1

If a piston is lowered thereby compressing the gas, then work is being done ON THE SYSTEM (gas) and the sign for work (w) is positive (+), so the answer would be (a).

Answer 2

Physics answer: The definition of work is simply a force moved through a distance. The units of work are Joules (same as energy). Physical compression of a cylinder head along a linear tube is a force moving through a distance. The work done by the piston on the gas is positive. The gas is compressed, and absorbs that energy. I believe the answer is a since that is consistent with physics and the thermodynamics conventions referenced below.

Thermodynamics has its own sign conventions.

If work is done on the system, its sign is positive.

If work is done by the system, its sign is negative.

https://www2.chem.wisc.edu/deptfiles/genchem/netorial/modules/thermodynamics/energy/energy4.htm#:~:text=If%20energy%20enters%20the%20system,system%2C%20its%20sign%20is%20negative.