Explanation

The smallest Republic in the world is Nauru

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Nauru is the third-smallest country in the world

Nauru is formerly known as Pleasant Island

Capital:                 Yaren

Currency:              Australian dollar

Continent:             Oceania

Area:                     20.98 km²

President            Russ Kun

Population:           12,704 (2018) World Bank

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while 

The smallest Muslim country is Brunei

Nauru is the smallest republic in the world

Maldives is the smallest in SAARC

Largest Muslim county Indonesia.