An SCR (Silicon Controlled Rectifier) is a four-layer (P-N-P-N) device with three junctions, J1, J2 and J3. Its behaviour is best understood through these junctions:

• Forward blocking state: The SCR is forward biased (anode positive with respect to cathode), but no adequate gate signal has been applied. The middle junction J2 is reverse biased, so it blocks current — the device stays OFF even though it is ready to conduct.
• Conduction state: Once a sufficient gate current is injected, J2 breaks down, the internal regenerative (positive feedback) action latches the device, and all three junctions conduct. The SCR is fully ON and stays ON even if the gate signal is removed.

The act of moving the SCR from forward blocking to full conduction by applying a gate pulse is called triggering (also known as firing or gate turn-on). This is the correct answer.

The other terms describe different processes: commutation is the opposite action — turning a conducting SCR OFF by reducing its current below the holding value. Avalanche breakdown refers to conduction forced by excessive voltage (forward breakover or reverse avalanche), which is an uncontrolled, potentially damaging turn-on rather than the intended gate-controlled one. Forward recovery relates to transient voltage behaviour when a device begins to conduct, not to the gate-initiated switching of an SCR into its ON state.