Generally seedless watermelon is

Correct option is B

Triploid watermelons are generally seedless. These watermelons are created by crossing diploid (2n) and tetraploid (4n) plants, resulting in sterile triploid (3n) offspring that cannot produce viable seeds.
Explanation of other options:
(a) Tetraploid: Used in breeding but not directly seedless.
(c) Diploid: Regular seeded watermelon varieties.