Where does the selective reabsorption of glomerular filtrate take place?

Which of the following statement$(s)$ is/are true?
$(1)$ Urine is hypertonic in the distal convoluted tubule.
$(2)$ When the urine passes into the collecting tubule,it becomes hypotonic.
$(3)$ Urine is isotonic in the proximal convoluted tubule.
$(4)$ Urine becomes more and more hypotonic as it passes through Henle's loop.

Reabsorption in the tubules of nephrons occurs by the process of

The high threshold substances are

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.

Transport of electrolytes through the loop of Henle takes place by: