The candidates, who attempted this question, responded well to parts (ai) and (aii).  However parts (aiii) and (b) were difficult for them.  The required responses to these parts are given below:

(aiii)     -           it requires large water passages to ensure unrestricted flow;
            -           it requires high radiator height or bulky radiator;
            -           it requires a big bonnet;
            -           it requires large quantity of water;
            -           water circulation is slow.

(b)       This refers to the circulation of water due to change in densities i.e. the hotter water moves to the top while the colder moves down.