Question

When a fuel is burnt, carbon dioxide (or carbon monoxide) and water vapour are given out. Can you name one fuel which burns without giving off water vapour? Why does it not give out water?

Answer 1

The fuel that burns without giving out water vapour is coke, which is a pure form of carbon. It has high carbon content and low amount of hydrocarbon.
Water vapour is released from a fuel if it contains hydrogen. However, coke has very low hydrogen content and hence, water vapour is not given out. It simply burns giving carbon dioxide gas.

$\mathrm{C}+O_2\underset{}{\overset{}{\to }}{\mathrm{CO}}_2$