The correct answer is option-2, Rs. 6,000. To calculate the cost of energy, we need to determine the total energy consumed by the refrigerator and then multiply it by the cost per kilowatt-hour.

Given that the refrigerator consumes 5 kW of power and operates for 10 hours per day for 30 days, we can calculate the total energy consumed using the formula:

Total Energy Consumed = Power × Time

Total Energy Consumed = 5 kW × 10 hours/day × 30 days

Total Energy Consumed = 1500 kWh

Now, to find the cost of energy, we multiply the total energy consumed by the cost per kilowatt-hour (Rs. 4):

Cost of Energy = Total Energy Consumed × Cost per kWh

Cost of Energy = 1500 kWh × Rs. 4/kWh

Cost of Energy = Rs. 6000

Therefore, the cost of energy to operate the industrial refrigerator for 10 hours per day for 30 days at a charge of Rs. 4 per kilowatt-hour will be Rs. 6,000.