Combustion and Flame — Important Questions

Carbon monoxide, because it is a colourless, odourless, highly poisonous gas.

Step 1: When a carbon-based fuel like coal burns in limited oxygen (incomplete combustion), carbon monoxide (CO) is produced instead of carbon dioxide (CO₂). Step 2: Complete combustion: C + O₂ → CO₂. Incomplete combustion: 2C + O₂ → 2CO. Step 3: Carbon monoxide is extremely dangerous because it is colourless and odourless – a sleeping person cannot detect it. Step 4: CO binds to haemoglobin in the blood (forming carboxyhaemoglobin) much more strongly than oxygen does, preventing the blood from carrying oxygen to body cells, leading to suffocation and death. Step 5: Option A – CO₂ is produced

Coal and diesel

Step 1: Acid rain forms when sulphur dioxide (SO₂) and nitrogen oxides (NOₓ) dissolve in rainwater to form sulphuric acid (H₂SO₄) and nitric acid (HNO₃) respectively. Step 2: Coal contains significant amounts of sulphur as an impurity. When coal burns, this sulphur combines with oxygen to form SO₂. Step 3: Diesel engines operate at high temperatures, causing nitrogen (N₂) and oxygen (O₂) from air to react and form oxides of nitrogen (NOₓ). Also, diesel itself contains sulphur compounds. Step 4: Coal and diesel together are the major contributors to acid rain through release of SO₂ and NOₓ. Ste

Spontaneous combustion

Step 1: Different types of combustion are classified based on the speed and conditions of burning. Step 2: Spontaneous combustion is the type in which a material suddenly bursts into flames without any apparent external cause (no flame or spark applied). The ignition temperature of the substance is at or below room temperature. Step 3: Example: White phosphorus undergoes spontaneous combustion in air at room temperature. Coal dust in mines can also undergo spontaneous combustion. Step 4: Rapid combustion refers to burning that produces heat and light quickly when ignited (e.g., burning of LPG

The luminous zone contains unburnt carbon particles that deposit on the glass.

Step 1: In the luminous (middle) zone of a candle flame, combustion is incomplete because not enough oxygen reaches this inner region. Step 2: Due to incomplete combustion, tiny solid carbon particles (soot) are produced and remain suspended in the flame. These particles get heated to a high temperature and glow, giving the flame its characteristic yellow luminous appearance. Step 3: When a glass plate is introduced into this zone, the unburnt carbon particles deposit on the cooler glass surface, forming a visible black ring. Step 4: This experiment conclusively proves the presence of unburnt