SCR can be turned on by

1. applying anode voltage at a sufficient fast rate
2. applying sufficiently large anode voltage
3. increasing the temperature of SCR to a sufficiently
4. applying sufficiently large gate current.

ANS:C - 1, 2, 3, 4

If we apply the anode voltage above breakover voltage of SCR, SCR can be triggered. Also by sufficiently fast rate of rise of anode voltage and large gate current will trigger SCR_on. During forward blocking most of the applied voltage appears across reverse biased junction J₂. This voltage across J₂ associated with leakage current may rise temperature of this junction. With increase in temperature, leakage current through junction J₂ further increases and this cumulative process may turn on the SCR at some high temperature.