Voltage dependent resistors are usually made from

Answer: Option B

Voltage dependent resistors (VDRs), also known as varistors, are semiconductor devices designed to protect electronic circuits from excessive voltage spikes and surges.

Silicon carbide is commonly used as the material for VDRs due to its properties:

1. Non-linear resistance: Silicon carbide exhibits a non-linear relationship between voltage and current, which allows it to act as a variable resistor that decreases its resistance as voltage increases beyond a certain threshold.

2. High breakdown voltage: Silicon carbide can withstand high voltages, making it effective for protecting circuits against transient overvoltage conditions.

Option A: Charcoal is incorrect because charcoal is not suitable for making VDRs due to its poor electrical properties.

Option C: Nichrome is incorrect because nichrome is an alloy used in heating elements due to its high electrical resistance and heat resistance, but it is not used in VDRs.

Option D: Graphite is incorrect because graphite is a good conductor of electricity and is used in electrodes and other applications requiring high electrical conductivity, not in VDRs.

Therefore, the correct answer is Silicon carbide.