Explanation:

- Swachh Bharat Abhiyaan is a government initiative focused on promoting cleanliness and sanitation in India.

- As part of this mission, each citizen is encouraged to contribute their efforts to maintain cleanliness.

- ?? Option:1, 70 - This option suggests individuals contribute 70 hours per year, but this is not the promoted expectation.

- ?? Option:2, 80 - This option suggests 80 hours, which is also not aligned with the campaign's call for action.

- ?? Option:3, 90 - Seemingly adequate, but not the correct expectation set by the initiative.

- ?? Option:4, 100 - The correct option. As per the Swachh Bharat Abhiyaan, people are expected to contribute 100 hours each year to cleanliness activities.