The correct answer is kilowatt-hour (kWh).

In domestic electricity billing, the energy consumption is measured in kilowatt-hours (kWh). One kilowatt-hour represents the energy consumed by a 1 kW appliance operating for one hour. It's a practical unit for measuring the energy used by households as it directly relates to power consumption over time. Other options are incorrect because they don't represent energy in the context of domestic electricity billing. Kilo Volt Ampere Hour (kVAh) is relevant for apparent power but not for actual energy consumption. Kilojoule-hour is an alternative energy unit, but kWh is the standard for billing purposes. Milliamp-hour (mAh) is used for smaller devices like batteries, not for household electricity.

The other options are not suitable because:

• Kilo Volt Ampere Hour (kVAh): This unit is used for apparent power, which is different from actual energy consumption (kWh).
• Kilo Joule Hour (kJh): Although this unit represents energy, kilowatt-hour (kWh) is the standard unit used by electricity companies for billing purposes.
• Milliamps Hour (mAh): This unit is primarily used for batteries and smaller devices, not for domestic electricity consumption.

Therefore, only the kilowatt-hour accurately reflects the unit of electrical energy consumption used in domestic tariffs.