In a thyristor $$dc$$ chopper which type of commutation results in best performance?

Consider the chopper circuit of figure. The chopper operates at $$400$$ $$Hz$$ and $$50$$% duty cycle. The load current remains almost ripple free at $$10A.$$ Assuming the input voltage to be $$200V$$ and the devices to be ideal, the turn-off time available to the thyristor $$Th$$ $$M$$ is____________ $$\mu s$$

A $$dc$$ to $$dc$$ transistor chopper supplied from a fixed voltage $$dc$$ source feeds a fixed resistive-inductive load and a free-wheeling diode. The chopper operates at $$1$$ $$kHz$$ and $$50$$% duty cycle. Without changing the value of the average $$dc$$ current through the load, if it is desired to reduce the ripple content of load current, the control action needed will be

Match the following

List $$-$$ $${\rm I}$$
$$A.$$ Commutation
$$B.$$ $$V$$ $$-$$ Curves
$$C.$$ Free wheeling diode
$$D.$$ Overlap

List $$-$$ $${\rm II}$$
$$P.$$ Resistive load
$$Q.$$ Inductive load
$$R.$$ Capacitive load
$$S.$$ Inter pole
$$T.$$ Source Inductance
$$U.$$ Synchronous motor