what is national income.explain with an example

National Income is the aggregate of factor incomes earned by all the factors of production (that are normal residents of a country) within the domestic territory and abroad. It is also known as Net National Product at Factor Cost.For various concepts of national income,refer to the below mentioned link.
https://www.meritnation.com/ask-answer/question/what-is-the-meaning-of-national-income-and-its-various-conce/national-income-accounting/1752766
Due to paucity of time, it would not be possible for us to answer all your queries. However, two of your questions have been answered by us.