Which article of the constitution of Pakistan is relevant to the national language?

Which article of the constitution of Pakistan is relevant to the national language?

پاکستان کے آئین کا کون سا آرٹیکل قومی زبان سے متعلق ہے؟
Explanation

According to Article 251 of the Constitution of Pakistan, Urdu is declared as the national language of Pakistan.

This article emphasizes the importance of promoting and developing Urdu as the lingua franca of the country.

It also allowing provincial languages to be used at the provincial level.