Final answer:
The work done by a gas is negative for an isochoric process since there is no change in volume and hence no work is performed by the gas.
Step-by-step explanation:
The work done by a gas is negative for an isometric process, also known as an isochoric process. This is because in an isometric or isochoric process, the volume of the system does not change, meaning there is no expansion or compression of the gas, and hence no work is done on or by the gas. Therefore, the work done is zero, which can be considered as not positive (though it is important to note that traditionally, 'negative work' implies movement opposite to the direction of force, which is not applicable here as there is no movement of the piston).