Explanation:

To understand why option B is the correct answer, let's first understand the working principle of an SCR (Silicon Controlled Rectifier).

Working Principle of SCR:
An SCR is a four-layer, three-junction semiconductor device that can control the flow of current. It consists of three terminals: anode, cathode, and gate. The anode is connected to the positive terminal of the power supply, the cathode is connected to the negative terminal, and the gate is used to control the SCR.

When a positive voltage (anode-cathode voltage) is applied across the SCR, it blocks the current flow in the forward direction. However, when a positive voltage is applied to the gate terminal with respect to the cathode, the SCR enters the ON state and starts conducting current. Once the SCR is triggered into conduction, it remains in the ON state until the anode-cathode current drops below a certain threshold called the holding current.

Analysis of Options:
a) Gate signal is continuously required: This option suggests that a continuous gate signal is necessary for the SCR to remain in the ON state. However, once triggered, the SCR remains conducting even if the gate signal is removed. Therefore, this option is incorrect.

b) No continuous gate signal is required: This option correctly states that no continuous gate signal is required for the SCR to remain in the ON state. Once triggered, the SCR will continue to conduct even if the gate signal is removed. This is because the triggering mechanism causes a regenerative process within the SCR, which sustains the conduction state.

c) No forward anode-cathode voltage is required: This option is incorrect. A forward anode-cathode voltage is necessary for the SCR to conduct current. Without the voltage, the SCR will remain in the blocking state.

d) Negative gate signal is continuously required: This option is incorrect. The gate signal required to trigger the SCR into conduction is usually positive with respect to the cathode. A negative gate signal is not required for the SCR to remain in the ON state.

Therefore, option B, "No continuous gate signal is required," is the correct answer.

B no continuous gate signal is required