Why is a small amount of urea retained in the kidney matrix?

What does the following figure represent?

If the kidneys fail to reabsorb water,what will be the effect on the tissues?

Indicate whether the following statement is true or false:
Henle's loop plays an important role in concentrating the urine.

If the kidneys fail to reabsorb water,what effect will be observed on the tissues?

Which of the following statements about the reabsorption process in Henle's loop are correct?
$(a)$ The descending limb of Henle's loop is permeable to water but almost impermeable to electrolytes.
$(b)$ Urine gets concentrated in Henle's loop.
$(c)$ Reabsorption of $Na^+$ and water takes place in Henle's loop.
$(d)$ Active or passive transport of electrolytes occurs in the ascending limb of Henle's loop.
Choose the correct answer from the options given below: