Where is the fuel shutoff valve located in a Cessna 172?

The fuel shutoff valve in a Cessna 172 is indeed located on the firewall, near the fuel strainer. This placement is crucial for safety and accessibility. The valve allows the pilot to quickly and effectively shut off fuel flow in case of an emergency or during maintenance, ensuring that there is no risk of fuel leakage in the engine compartment. By situating the valve on the firewall, it can be reached easily from the cockpit, allowing for quick action without needing access to the passenger area or fuel tank locations.

The other options are incorrect because they suggest locations that do not align with the design and safety considerations of the aircraft. For instance, placing the valve under the passenger seat would be less accessible in emergency situations, and having it in the cockpit overhead panel or near the fuel tank would unnecessarily complicate the fuel system's operation and maintenance accessibility. Thus, option B aligns with the standard design practices for enhancing pilot control and safety in the Cessna 172.