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

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:

The concentration of urine depends upon $........$.

What is the counter current mechanism?

Which one of the following animals has a longer loop of Henle?

We can produce a concentrated urine. This is facilitated by a special mechanism. Identify the mechanism.