High threshold substances are the substances which can be

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

The complete reabsorption of glucose occurs in the ........

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.

In which part of the nephron are the majority of electrolytes and water ($70$ to $80\%$) reabsorbed from the glomerular filtrate?

Components reabsorbed by the Proximal Convoluted Tubule $(PCT)$ - $P$
Components secreted by the Proximal Convoluted Tubule $(PCT)$ - $Q$
$I - K^{+}$,$II - \text{Ammonia}$,$III - HCO_{3}^{-}$,$IV - \text{Essential nutrients}$,$V - 70$ to $80\%$ $\text{electrolytes and water}$,$VI - H^{+}$
Select the correct option for $P$ and $Q$.
$P \quad\quad\quad Q$