Step 1: Understanding the Concept.
Part XVII of the Constitution deals with official languages, and specific articles within it cover different aspects, such as the language of the Union, of states, and of courts.
Step 2: Check the options.
Article 345 deals with the official language(s) of a state, not the Union, so option A is wrong. Article 348 deals with the language to be used in the Supreme Court, High Courts, and for Acts and Bills, so option C is wrong. Article 334 deals with reservation of seats for SCs, STs, and the Anglo-Indian community, an unrelated topic, so option D is wrong.
Step 3: Final Answer.
Article 343 declares Hindi in Devanagari script as the official language of the Union, so option B is correct.