Explanation:

- Depreciation reflects the gradual reduction in value of a fixed asset over its useful life for accounting purposes.

- Option 1: Deferred revenue expenditure - Incorrect, as depreciation is not intended to be spread across future financial years in the same way.

- Option 2: Capital expenditure - Refers to the initial investment in acquiring fixed assets, not their ongoing depreciation.

- Option 3: Capital gain - This relates to profit from the sale of assets, which is not relevant to depreciation.

- Option 4: Revenue expenditure/expense - Correct, depreciation is considered a revenue expense as it represents the cost of using an asset within the period.