Energy = Power × Time

Steps:

• Convert power to kilowatts: 1000 W = 1 kW.
• Convert time to hours: 30 minutes = 0.5 hours.
• Apply formula: Energy (kWh) = power (kW) × time (h) = 1 × 0.5 = 0.5 kWh.
• Voltage is irrelevant since power is given directly.

Why B is correct:

• Kilowatt-hour measures energy as power in kW multiplied by time in hours, yielding 0.5 kWh here.

Why the others are wrong:

• A: Incorrectly converts time, e.g., treating 30 minutes as 0.3 hours.
• C: Assumes full 1-hour operation instead of 0.5 hours.
• D: Misuses voltage or applies unrelated multiplication, like 1000 W × 12.

Final answer: B