Is "He studies in an university" correct?

Why

Deepak's rule — "an" before vowel letters — works correctly most of the time: an apple, an elephant, an orange. But the real rule underneath "a"/"an" is actually about SOUND, not spelling, and "a"/"an" letter-spotting is just a shortcut that happens to work in most, not all, cases. "University" is spelled starting with the vowel letter "u", but it's actually PRONOUNCED starting with a "y" consonant sound ("yoo-nih-VER-sih-tee"), and "an" is chosen based on how a word SOUNDS at the start, not how it's spelled. Since "university" starts with a consonant sound despite its vowel spelling, it takes "a", just like any other consonant-sounding word. Test: the reverse also happens — "hour" is spelled with a consonant letter "h", but the "h" is silent, so it's pronounced starting with a vowel sound, which is exactly why it's "an hour", not "a hour". His sister is right: "a"/"an" follows the sound at the start of a word, not the spelling, which is why it's "a university" despite the vowel letter.