Class A
The amplifier conducts current throughout the entire cycle (360º). The Class A design is the most inefficient and is used in low-power applications as well as in very high-end stereo. Such devices may be as little as 15% efficient, with 85% of the energy wasted as heat.
Class B
The current flows only 180º for half the cycle, or two transistors can be used in a push-pull fashion, each one operating for 180º. More efficient than Class A, it is typically used in low-end products.
Class AB
Combines Class A and B and current flows for 180º to 200º. Class AB designs are the most widely used for audio applications. Class AB amplifiers are typically about 50% efficient.
Class C
Operating for less than half of one wave cycle (100º to 150º), Class C amplifiers are the most efficient, but not used for audio applications because of their excessive distortion.
So it is chart 2.