On top of the list is Qatar. According to the laws in Qatar, they do not permit dual nationality, necessitating the renunciation of one's original passport.

Vatican City, the world's smallest country only grants citizenship under three exceptional circumstances- if one is a cardinal residing in Vatican, serves as a diplomat or employes within the Church.

Nestled between Austria and Switzerland, the affluent microstate of Liechtenstein, with its approximately 40,000 citizens, demands an extensive timeline for acquiring citizenship.

Bhutan maintains stringent acquiring citizenship is even more challenging. Foreigners seeking Bhutanese citizenship must reside in the country for a minimum of 20 years before applying.

Saudi Arabia, the oil-rich country presents formidable hurdles for those seeking citizenship. Candidates must have resided in the country for 10 years and possess fluent Arabic language skills.

Neighbouring Saudi Arabia, Kuwait, another oil-rich country. Candidates must have resided in Kuwait for a minimum of 20 years, know Arabic, and adhere to the Islamic faith.

Switzerland has one of Europe's most stringent citizenship processes. Foreigners must reside in the country for a minimum of 10 years and proficient in one of Switzerland's national languages.

China as mentioned by the Immigration Department, provides limited avenues for foreigners to acquire citizenship, primarily through family ties or "other legitimate reasons.

North Korea does not recognize dual citizenship, making it one of the most challenging countries to obtain citizenship, even though its desirability is limited.