The correct answer is option 4: Interest Payments.

Option 1: Defence refers to the spending on the military and defense-related activities. While defense expenditure is significant, it is not the most important item of expenditure on the revenue account.

Option 2: Subsidies are financial assistance provided by the government to individuals or organizations to support certain sectors or activities. While subsidies are an important part of government spending, they do not typically make up the largest portion of the expenditure on the revenue account.

Option 3: Pensions refer to regular payments made to retired government employees. While pensions are a significant expense for the government, they are not the most important item of expenditure on the revenue account.

Option 4: Interest Payments are the payments made by the government on the interest accrued on its borrowings, such as loans and bonds. These payments can be a substantial burden on the government`s finances and usually account for a significant portion of the expenditure on the revenue account. The interest payments represent the cost of borrowing for the government, which is crucial for managing its debt and overall financial stability.