An excessively lean air mixture may cause which of the following issues?

An excessively lean air-fuel mixture refers to a condition where there is a higher ratio of air to fuel than what is optimal for combustion. This lean mixture can lead to pre-ignition and detonation in internal combustion engines.

Pre-ignition occurs when the air-fuel mixture ignites before the spark plug fires, which can lead to knocking. Detonation, on the other hand, is an uncontrolled explosion of the air-fuel mixture within the cylinder, happening after the spark plug has fired, and is characterized by a rapid rise in cylinder pressure. Both phenomena can cause significant engine damage over time, including damage to pistons, rings, and valves due to excessive pressure and temperature.

The other options, while related to fuel or engine performance issues, do not particularly arise as a direct result of an excessively lean mixture. Fuel starvation typically refers to a lack of sufficient fuel, and while an excessively lean mixture might suggest inadequate fuel, it is more about the balance of the mixture. Excessive smoke output typically results from an overly rich mixture, not a lean one. Complete engine failure is a severe consequence that could result from various issues but is not as directly connected to a lean mixture as pre-ignition and detonation. Therefore