Explanation:

- Speaker: The Speaker presides over the Lok Sabha but does not have the authority to sanction public expenditure.

- President: The President authorizes the withdrawal of funds from the Consolidated Fund of India, but only after Parliament has approved the expenditure.

- Prime Minister: The Prime Minister heads the government but does not have the final constitutional authority to sanction public expenditure.

- Parliament: Parliament holds the final authority to approve and sanction the expenditure of public money through the passage of Appropriation Bills and other financial legislation.

The correct answer is Option:4, Parliament.