The voltage of the single phase supply to residential consumers is

The correct answer is C. 230 V.

Single-phase power is the most common type of power used in homes and businesses. It is supplied by two wires, one hot and one neutral. The voltage between the hot and neutral wires is 230 V in most countries.

Option A is incorrect because 110 V is the voltage of a single-phase supply in some countries, but not in most.

Option B is incorrect because 210 V is not a standard voltage for a single-phase supply.

Option D is incorrect because 400 V is the voltage of a three-phase supply, not a single-phase supply.