The major excretory product of arthropods is

Uric acid is the nitrogenous excretory product in $...$.

Which of the following excretes urea?

The characteristic that is shared by urea,uric acid and ammonia is/are:
$I.$ They are nitrogenous wastes.
$II.$ They all need very large amount of water for excretion.
$III.$ They are all equally toxic.
$IV.$ They are equally in the kidneys.

Fill in the gaps:
$A$ healthy adult human excretes (on an average) ............ $gm$ of urea/day.

In ureotelic animals,where does the conversion of ammonia into urea take place?