Choose the odd one out and write the category of the remaining terms

Dear student,
Please find below the answer:

a. ​​​​Neuron is the odd one out. Rest of the terms are related to the excretory system.
b. Excess sodium chloride is the odd one out. Rest of the terms are types of nitrogenous waste products.
c. Loop of Henle is the odd one out. Rest all are parts of the kidney.
d. Papilla is the odd one out. Rest of the parts are involved in the production of urine directly.

Hope this clears your doubt.
Regards.