Why is applying full power essential during a go-around?

Applying full power during a go-around is essential primarily because it ensures sufficient thrust to overcome drag. During a go-around, the aircraft needs to quickly transition from a descent phase back to a climb. This requires a significant amount of thrust to not only counteract the drag produced by the aircraft at a lower configuration (such as landing gear extended and flaps deployed) but also to gain altitude safely and efficiently.

In a go-around situation, missing or inadequate thrust could lead to a stall or an inability to climb effectively, especially if the aircraft is still heavy with fuel or cargo. Therefore, full power is necessary to provide the required performance to safely maneuver the aircraft back into a climb while adjusting for any potential changes in configuration and ensuring a safe margin above stall speed.

The other options, while related to aspect of flight, do not capture the primary need for full power during a go-around. For instance, maintaining optimal fuel efficiency is typically not a priority during such an emergency maneuver, as the focus is on safety and regaining altitude.