Step 1: Understand each condition.
Arthritis: An inflammation of joints, affecting bones.
Gout: A form of arthritis caused by uric acid crystals in the joints.
Rickets: A bone disease caused by vitamin D deficiency, affecting bone development.
Leukemia: A type of cancer that affects blood cells, not directly related to bones.
Step 2: Hence, the correct answer is (4) Leukemia, as it is not a bone disease.