Explanation:

- In India, the minimum age for employment in a factory is 14 years.

- This is governed by the Child Labour (Prohibition and Regulation) Act of 1986.

- However, restrictions apply to the type and hours of work young people can undertake.

- 14 years is the correct age, aligning with international labor standards in some cases.

- Although they can work, there are conditions and protections in place for their health and education.

- 18 years is often required for hazardous work but not general factory work.

- 21 years is not a standard minimum employment age in India; it's more common for specific professions or responsibilities.

- 16 years is notably considered for some types of work but is not predominant for factory employment rules.

Correct Answer: Option 3, 14 years