Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R)
Assertion (A) : Ascending limb of loop of Henle is impermeable to water and allows transport of electrolytes actively or passively.
Reason (R) : Dilution of filtrate takes place due to efflux of electrolytes in the medullary fluid.
In the light of the above statements, choose the correct answer from the options given below.

(A) is true. The ascending limb of the loop of Henle is impermeable to water. It transports electrolytes out of the tubule through active transport as well as simple diffusion (passive transport).

(R) is also true. Dilution of the fi ltrate occurs as electrolytes, primarily sodium and chloride ions, are actively transported out of the ascending limb into the medullary interstitium. 

* Note: Actually, (R) does not directly explain why the ascending limb is impermeable to water. The impermeability of the ascending limb to water is primarily due to the absence of aquaporin channels.