Revenue expenditure refers to the day-to-day expenses incurred by a business or government that are not capitalized but are instead expensed immediately.

Revenue expenditure includes costs that are incurred for the normal operating activities of the organization and are essential for generating revenue in the short term.

Revenue expenditure does not result in the creation of a fixed asset or an increase in the earning capacity of the organization. Instead, it is used to maintain the existing level of operations.

Let's analyze the given options to identify revenue expenditure:

- Purchase of shares of PSUs: This involves buying shares of Public Sector Undertakings (PSUs), which are considered investments rather than day-to-day operating expenses. Therefore, this is not a revenue expenditure.

- Loan and advancement: Providing loans or advances can be considered revenue expenditure if they are meant for short-term financial assistance to individuals or businesses. However, this expenditure is usually classified as a capital expenditure because it involves lending money that is expected to be repaid with interest.

- Subsidies given to the public: Subsidies provided to the public are considered revenue expenditure as they are recurring expenses incurred by the government to support certain sectors or individuals. These subsidies do not result in the creation of an asset and are essential for maintaining social welfare programs.

- Expenditure on acquisition of land: Acquiring land involves a significant investment and leads to the creation of a fixed asset. Therefore, expenditure on the acquisition of land is classified as a capital expenditure rather than revenue expenditure.

In conclusion, subsidies given to the public is the revenue expenditure among the options provided.