Naturalization
From VjWiki - The Immigration Wiki
A United States Permanent Resident can petition the USCIS to become a US Citizen through a process call Naturalization.
Most Permanent Residents must wait five years after getting their Green Card to petition to become a US Citizen however a spouse of a US Citizen can apply for citizenship three years after approval of their Adjustment of Status. The five or three year time frame does not include any time spent outside of the United States on travel.
Note: If you came to the United States on a K2 visa, you can apply for citizenship 5 (five) years after approval of Adjustment of Status, as only spouses of US Citizens are eligible to apply for Naturalization after 3 years. However, if a K2 is very young, it is possible that they may be naturalized along with the parent, if the parent becomes naturalized before the K2 turns 18.
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