The countercurrent arrangement of the two limbs of the loop of henle becomes a multiplier of electrolyte concentration due to which other characteristic?

Out of the following given choices;

A. water permeability of the descending limb

B. water impermeability of the ascending limb

C. active transport of electrolytes out of the ascending limb

D. thickness of the ascending limb

The answer is A. This descending loop of Henle has low permeability to ions. This is converse to the thin ascending limp that is impermeable to water but actively takes up ions. This ensure that the interstitial fluid in the region (ascending limb) is of high osmotic pressure hence water moves from the tubules and therefore makes the urine in the tubules more concentrated.