(a) Burning of wood and coal causes pollution of air.
(b) A liquid fuel, used in homes is LPG.
(c) Fuel must be heated to its ignition temperature before it starts burning.
(d) Fire produced by oil cannot be controlled by water.
(a) The most important pollutants of burning firewood are particulate matter (PM), soot or black carbon which are potentially carcinogenic(cancer causing) compounds. Wood burning generates nitrogen oxide and carbon monoxide which are major air pollutants. Burning of coal results in emission of sulfur dioxide (SO2), which contributes to acid rain and respiratory illnesses, nitrogen oxides (NOx), which contribute to smog and respiratory illnesses, carbon dioxide (CO2), which is the primary greenhouse gas.
(b) The main reason behind LPG being a popular choice of fuel for domestic use, is that it promises a low level of fuel consumption. LPG equipments do not demand high maintenance and it also has a narrow range with respect to flammability.
(c) Ignition temperature is the minimum temperature to which a combustible substance must be heated, before it catches fire. A combustible substance cannot catch fire as long as its temperature is lower than its ignition temperature.
(d) Water cannot put off fire produced by oil because water is heavier than oil. It settles down or sinks below the oil particles and thus cannot bring the ignition temperature of the substance down. Hence, oil keeps on burning on the top.