(a) When wood burns, the carbon present in it is oxidised to carbon dioxide (C0₂), which is a non-poisonous gas. When the windows are closed, the air or oxygen cannot enter the room. In the incomplete supply of oxygen, carbon is oxidised to carbon monoxide (CO) which is a highly poisonous gas. It caused suffocation in a closed room. On opening the windows, the poisonous gas slowly diffused out the room and fresh air came inside.  
(b) Mohan is quite intelligent, quick in decisions and caring about his family.

The head of the safety match contains antimony trisulphide and potassium chlorate. The rubbing surface has powdered glass and a little red phosphorus. When the match is struck against the rubbing surface, some red phosphorus gets converted into white phosphorus. This immediately reacts with potassium chlorate in the matchstick head to produce enough heat to ignite antimony trisulphide and start combustion.

(i) Combustible - charcoal, straw, cardboard, paper, candle, wood.
(ii) Non-combustible - chalk, stone, iron rod. copper coin, glass.

CNG has replaced diesel and petrol as fuel in automobiles because petrol and diesel produced a lot of unburnt carbon particles and emitted carbon dioxide, nitrogen oxides and sulphur dioxide. These all gases are poisonous gases and cause various environmental hazards. The main causes of acid rain are nitrogen oxides and sulphur dioxide. But CNG is safe because it produces these substances in very small amounts. Thus, the use of CNG is reducing pollution in our cities.

It has low calorific value and causes a lot of pollution.

The different zones of a candle are innermost, middle and outermost zone.

Two fuels which we use in our homes for cooking food are LPG and kerosene oil.

The substances which undergo combustion are called combustible substances.

The substance which provides heat and light is called fuels

Three essential requirements to produce fire are as follows:
(i) Fuel
(ii) Air and
(iii) Heat to acquire the ignition temperature. The job of fire extinguisher is to cut off the supply of air or to bring down the temperature of fuel or both. The most common fire extinguisher is water. But water works only when things like wood and paper are on fire. For fires involving electrical equipment and inflammable materials like petrol, carbon dioxide (C0₂) is the best extinguisher. CO₂ being heavier than oxygen, covers the fire like a blanket. Since, the contact between the fuel and oxygen is cut-off, so the fire can be controlled. The added advantage of CO₂ is that in most cases, it does not harm the electrical equipment.

Reasons of forest fires are
(i) At high temperature, sometimes dry grass catches fire which spreads throughout the forest.
(ii) Campfire may also be a reason.
(iii) Lightning.
(iv) The use of fires by villagers to ward off wild animals.
(v) Fire lit intentionally by people living around forests for recreation.
(vi) Fires started accidentally by careless visitors to forests how discard cigarette butts.
(vii) The friction of bamboos due to high wind velocity and rolling stones.

Pouring water to extinguish the fire due to oil was not suitable action. It is because oil is lighter than water. So, water will settle down below the oil. In such condition, sand or soil should be used. They cut off the supply of air to the fire. Thus, fire can be controlled. But sand or soil will not be available at that place. So, Manu should have switched off the flame of the burner and put a lid on the frying pan. By doing this, the contact between fuel and oxygen is cut off and the flame will go off.