Page 1 :
Question 1., , List conditions under which combustion can, take place., , Answer:, , Combustion can take place in the presence of:, (a) a combustible substance., , (b) oxygen, that is, the supporter of, combustion., , (c) attainment of ignition temperature of the, substance.

Page 2 :
Question 2., , Fill in the blanks., , (a) Burning of wood and coal causes _____ of, air., , (b) A liquid fuel, used in homes is ______, , (c) Fuel must be heated to its _______, starts burning., , (d) Fire produced by oil cannot be controlled, , Answer:, , (a) pollution, , (b) LPG, , (c) ignition temperature, (d) water

Page 3 :
Question 3., , Explain how the use of CNG in automobiles, has reduced pollution in our cities., , Answer:, , The use of CNG in automobiles has reduced, pollution in our cities as it is a quality fuel and, has some benefits:, , (a) It gives out less carbon dioxide gas,, carbon monoxide gas, sulphur dioxide and, nitrogen dioxide, which is beneficial as they, play crucial role in global warming and acid, rain., , (b) It leaves behind no residue after its, combustion.

Page 4 :
Question 4., Compare LPG and wood as fuels., Answer:, , LPG Wood, , (i) It does not cause, (i) It pollutes air on, , pollution on, , its combustion., combustion., (ii) No smoke is (ii) It produces, produced. smoke., , (iii) Itis a liquid fuel. | (iii) It is a solid fuel., , (iv) It has more (iv) It has less, calorific value calorific value, , (55000 kJ/kg). (17000 kJ/kg).

Page 5 :
(iv) It has more, calorific value, , (55000 kJ/kg)., , (v) It can be easily, transported, as itis, , Stored in cylinders., , , , (iv) It has less, calorific value, , (17000 kJ/kg)., , (v) It can't be, transported easily, , like LPG fuels.