Concept:A non-restrictive clause adds extra information and must be set off by commas on both sides.Explanation:The phrase "who lives in Delhi" is non‑essential. Removing it leaves "My friend is visiting me," which is still complete. Therefore, commas go before and after the clause. Option B correctly uses a comma before "who" and another after "Delhi". Option A wrongly places a comma between "visiting" and "me". Option C puts a comma after "who" and at the end, disturbing flow. Option D uses only one comma after "Delhi", breaking the balance.Answer:Option B