What is the range of osmolarity from the renal cortex to the inner medulla?

Human urine as compared to human blood is

The concentration of sodium and chloride ions is lowest in which of the following regions?

To maintain the required osmotic concentration in the medullary interstitium of the kidneys of ureotelic animals,some amount of ..... is retained.

$A$: The final reabsorption of water from urine into blood occurs through the collecting duct of a mammalian nephron,resulting in the production of hyperosmotic urine.
$R$: The loop of Henle is responsible for the formation of a sodium gradient across the depth of the medullary interstitium of a mammalian kidney.

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