The correct answer is option 4: Net National Product at factor cost.

To understand why it is the equivalent to National Income, let`s break down each option:

Option 1: Gross Domestic Product (GDP) at market prices refers to the total value of all goods and services produced within a country`s borders. While GDP gives us an idea of the overall economic activity, it includes both domestic and foreign factors and does not solely represent the income generated within the country.

Option 2: Net Domestic Product (NDP) at factor prices is the value of goods and services produced within a country minus depreciation. It is a measure of the net value added by the domestic factors of production. However, it does not take into account income generated by foreign factors.

Option 3: Net National Product (NNP) at market prices is the value of goods and services produced by the residents of a country, also considering depreciation. NNP includes both domestic and foreign factors but still does not represent the income of the country.

Option 4: Net National Product (NNP) at factor cost is the value of goods and services produced by the residents of a country, including depreciation and only considering income generated within the country`s borders. It represents the income earned by the factors