1. Orange: A widely consumed citrus fruit known for its sweet and tangy flavor.
2. Lemon: Popular for its sour taste, used in beverages and cooking.
3. Grapefruit: A larger citrus fruit with a bittersweet taste, rich in nutrients.
4. Lime: A small, sour citrus fruit often used in drinks and culinary dishes.
Citrus fruits are rich in vitamin C and antioxidants, making them essential for a healthy diet.
Assertion (A): The sum of the first fifteen terms of the AP $21, 18, 15, 12, \dots$ is zero.
Reason (R): The sum of the first $n$ terms of an AP with first term $a$ and common difference $d$ is given by: $S_n = \frac{n}{2} \left[ a + (n - 1) d \right].$