Explanation:

- Given: 24 persons working 8 hours a day can complete 2 units of work in 10 days.

- Calculate total work in "person-hours": \(24 \times 8 \times 10 = 1920\) person-hours for 2 units.

- Therefore, 1 unit of work requires \(\frac{1920}{2} = 960\) person-hours.

- For 4 units, total work required is \(960 \times 4 = 3840\) person-hours.

- New scenario: work for 6 hours a day for 16 days.

- Calculate total available hours: \(6 \times 16 = 96\) hours per person.

- Required workers: \(\frac{3840}{96} = 40\).

- Correct Option: 40 persons

- Answer: Option 1: 40