A) In the PCT, filtrate is isotonic to blood plasma as there is an equal exchange of ions.
H+ and
NH3 are secreted into the PCT while
K+,
HCO−3 and
NaCl are reabsorbed into the interstitial cells.
B) The ascending limb of Henle's loop opens into the DCT.
C) In the descending limb of the loop of Henle, the fluid is hypertonic to blood plasma as there is a greater concentration of ions and a lesser concentration of water.
D) The ascending limb of the loop of Henle is impervious to water, so all the electrolytes diffuse out and the filtrate gets diluted.
So the correct answer is 'A-4, B-1, C-2, D-3'.