Which one of the following is also known as resonant commutation?

Solution:-
Class A commutation is also known as load commutation or resonant commutation or self commutation. It is called so because components connected with loads create favourable condition for turning off the thyristor.

For achieving load commutation of a thyristor, the commutating components I and C are connected as shown in fig. 1 and fig. 2

Fig. 1 is suitable when the value of load resistance is low.

Fig. 2 is suitable when the value of load resistance is high.

The esential requirement for both the circuit is that the overall circuit must  be underdamped.

Class-A commutation is prevealent in thyristor circuits supplied from a dc source. This commutation is possible in dc circuits and not in ac circuits.