Which one of the following substances is actively secreted into the glomerular filtrate of the kidney tubule?

Select the $CORRECT$ statements:
$i$. Tubular secretion involves secretion of $H^{+}$ ions in $PCT$.
$ii$. Augmentation involves secretion of $H^{+}$ ions in $DCT$ and $CT$.
$iii$. Augmentation plays an important role in regulation of $pH$ of blood.
$iv$. Glomerular filtrate as well as urine are acidic.

Classify the following substances as actively or passively transported during the reabsorption of $GFR$: glucose,amino acids,nitrogenous wastes,$Na^+$,water.

Under normal conditions,which substance is completely reabsorbed in the renal tubules?

The maximum reabsorption of glomerular filtrate occurs in $:-$

Which part of the nephron transports a small amount of urea into the medullary interstitium to maintain the osmolarity?