Proportional tax is a tax whose

A proportional tax is a tax whose percentage rate remains constant as the tax base increases. This means that everyone pays the same percentage of their income or property value in taxes, regardless of how much money or property they have. For example, if the tax rate for a proportional tax is 10%, then someone who earns $10,000 per year would pay $1,000 in taxes, while someone who earns $100,000 per year would pay $10,000 in taxes. The percentage rate of the tax remains the same (10%), but the amount of taxes paid increases as the tax base (income) increases. Therefore, the correct answer is - "percentage rate remains constant as the tax base increases".