Option 1: 1

This option suggests that only 1 unit of energy is consumed in 30 days. However, this is incorrect as the use of a 100 W electric bulb for 10 hours a day would consume more energy than just 1 unit in 30 days.

Option 2: 10

This option suggests that 10 units of energy are consumed in 30 days. Although it is a plausible estimate, it is not the correct answer.

Option 3: 30

This option is the correct answer. It states that 30 units of energy are consumed in 30 days. Since the bulb is used for 10 hours a day, it consumes 100 W * 10 hours = 1000 Wh of energy in a day. To convert this to units, we divide by 1000 to get 1 unit per day. Therefore, in 30 days, the bulb consumes 30 units of energy.

Option 4: 300

This option suggests that 300 units of energy are consumed in 30 days. However, this is not the correct answer as it overestimates the energy consumption.

In conclusion, the correct answer is option 3, which states that 30 units of energy are consumed in