The mechanism of uric acid excretion in a nephron is:

What is the duct of Bellini?

$I.$ Reabsorption of water occurs passively in the initial segment of nephron.
$II.$ Nitrogenous wastes are absorbed by active transport.
$III.$ Conditional reabsorption of $Na^{+}$ and water takes place in $DCT$.
$IV.$ $DCT$ reabsorbs glucose.
$V.$ $DCT$ is capable of selective secretion of $H^{+}$,$K^{+}$ and $NH_{3}$ to maintain $pH$ and $Na^{+}-K^{+}$ balance in blood.
$VI.$ Substances like glucose,amino acids,$Na^{+}$,etc.,in the filtrate are reabsorbed actively.
Choose the option with incorrect statements.

In which part of the nephron are all essential nutrients and $70-80 \%$ of electrolytes and water reabsorbed?

What is the "renal threshold"?

Which of the following pairs is incorrect?