Which of the following substances is totally reabsorbed through renal tubules?

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 $Q$.
$P \quad\quad\quad Q$

The efferent arteriole emerging from the glomerulus forms a fine capillary network around the renal tubule, which is called .......

In which segment of the nephron,reabsorption is minimum?

Out of the following:
$I.$ $PCT$
$II.$ $DCT$
$III.$ Loop of Henle
$IV.$ Collecting duct
Which contributes most in maintaining the $pH$ of blood?

Which one of the following is mismatched?