The alphabet is a collection of letters, e.g. The English/Roman/Latin alphabet contains 26 letters.
Incorrect: “Marathi uses the Devanagari script and contains 52 alphabets.”
Correct: “The Marathi alphabet uses the Devanagari script and contains 52 letters.”
Here is a typical error, in this case made by one Aditi Phadnis in the Business Standard.