Belgrade is the capital, and Serbian in Cyrillic script is in official use under the Constitution
Background
Article 9 of Serbia's Constitution says the capital city of the Republic of Serbia is Belgrade.
Article 10 says the Serbian language and Cyrillic script are in official use.
The official use of other languages and scripts is regulated by law based on the Constitution.
Article 11 declares Serbia a secular state: churches and religious communities are separated from the state.
No religion may be established as a state or mandatory religion.
Capital:
Belgrade (Article 9)
Official language and script:
Serbian, Cyrillic (Article 10)
State character:
Secular (Article 11)
Why it matters for exams: Capital, official language and script are staple basic-fact questions for any country in the country-focus section.
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In plain words
Cyrillic Cyrillic script — The alphabet Serbia's Constitution names for official use alongside the Serbian language.