To solve this problem, we need to find the work done by the gas along the path $bc. \\ \\$The given diagram is a pressure-volume (P-V) graph. The work done by the gas during a process is given by the area under the curve on a P-V diagram.$\\ \\$For the path $bc,$ the process is at constant volume (isochoric process), as the volume remains constant at $400 \,$cm$^3. \\ \\$In an isochoric process, the work done $(W)$ is zero because there is no change in volume.$\\ \\$Therefore, the work done by the gas along the path $bc$ is:$\\ W = 0 \\ \\$This corresponds to Option 3: Zero.