Explanation:

- Preliminary expenses refer to costs incurred during the formation or establishment of a company.

- Option 1: Capital expenditure - Involves spending on acquiring or improving fixed assets, not typically associated with preliminary expenses.

- Option 2: Capital gain - Refers to profit from selling an asset, unrelated to preliminary expenses.

- Option 3: Deferred revenue expenditure - Correct. Preliminary expenses are capitalized and amortized over time, fitting the category of deferred revenue expenditure as they provide benefits over multiple years.

- Option 4: Revenue expenditure/expense - Typically involves day-to-day operational costs, not the nature of preliminary expenses.