The correct option is D Monocyte
A lymphocyte is a small leukocyte with a single round nucleus.
Neutrophil is another type of leukocyte which has multi-lobed nucleus, generally 2-5 lobes.
Basophils are granulocytes (WBC) and have the nucleus which is bi-lobed.
Monocyte is a large phagocytic WBC with a bean-shaped or kidney-shaped nucleus.
Therefore, the correct answer is option D.