A hard material $$X$$ which is mined from the earth is used as household fuel and also for the generation of electricity at thermal power stations. A soft material $$Y$$ is also used as a fuel in the form of candles. A gaseous material $$Z$$ which occurs along with petroleum is increasingly being used as a fuel in running vehicles in its compressed form.
(a) What are materials, $$X, Y$$ and $$Z$$?
(b) When materials $$X, Y$$ and $$Z$$ are burned separately:
(i) Which material burns by producing a yellow, luminous flame?
(ii) Which material ultimately burns without producing a flame?
(iii) Which material can burn in a gas stove by producing a blue flame?
(a). $$X$$ is coal, $$Y$$ is wax, and $$Z$$ is natural gas.
(b).
(i) $$Y$$ (wax) is the material that burns by producing a yellow, luminous flame.
(ii) $$X$$ (coal) is the material that ultimately burns without producing a flame.
(iii) $$Z$$ (natural gas) is the material that can burn in a gas stove by producing a blue flame.