The correct answer is option 4: retirement pension

1. Old age pension: Old age pension refers to regular payments made to retired individuals, usually by the government or pension plans. This payment represents a transfer of income and is not included in national income.

2. Gambling: These are transfers of money between individuals and don't reflect the creation of new goods or services.

3. Second-hand cars: Second-hand cars represent the sale of used goods and are typically not included in national income calculations. National income focuses on the production of new goods and services within a country's borders during a specific period.

Note: Retirement pensions paid by the government to its employees are typically considered a part of national income estimation rather than being classified as transfer payments. These pensions are a form of compensation for services rendered by the employees during their working years. While they may be provided unilaterally by the government, they are linked to the factor services (i.e., labor) provided by the employees and are thus regarded as a component of national income.