(i) Ammonia, urea and uric acid.
(ii) Yes, the amount of water expulsion depends upon the length of the loop of Henle (i.e., both are inversely proportional to each other).
(iii) Different animal groups present a variety of excretory structures (organs) to perform the process of excretion. In most of the invertebrates, these are simple tubular forms whereas, vertebrates have complex tubular organs called kidneys.
(iv) The teacher is very responsible towards his duty and he is trying to incorporate good values among his students.