Answer:
A person can acquire the citizenship of a country in four ways. By birth- a person's citizenship is decided at the time of his/her birth. For example- if you are born in India you will naturally acquire the citizenship of India, without considering the nationality of the parents. Therefore, birth is the main factor in acquiring citizenship.
By inheritance- in this method, an individual gets citizenship considering the nationality of his/her parents. For example- those who are born in India after 26th January, 1950 to Indian families staying outside the country, he/she is eligible to get citizenship of india.
By registration- a person can acquire citizenship by the means of submission of a prescribed application to the concerned office. That means, if an individual wants to become an Indian citizen, they have to fill some form followed by certain procedures and submit it to the office.
For example- those who are residing in India for a minimum of 5 years can get citizenship by registration.
By incorporation- If one country has merged or incorporated with another country, the citizenship of the incorporated country can be acquired. Generally, a country gets incorporated by means of war or voluntarily.
For example- Goa, Sikkim, Puducherry and Daman and Diu became part of India and their population got the citizenship of india.