____ is a colourless, odourless and toxic gas, produced when organic materials like natural gas coal or wood are incompletely burnt. 

Concept:

A colourless, odourless, and toxic gas produced when organic materials like natural gas, coal, or wood are incompletely burnt is known as carbon monoxide. This gas is dangerous as it can interfere with the blood's ability to carry oxygen.

Explanation of Options:

• Sulphur dioxide (SO₂): A pungent-smelling, colourless gas produced by the combustion of fossil fuels containing sulfur. It is not odourless.
• Carbon monoxide (CO): A colourless, odourless, and toxic gas produced during the incomplete combustion of organic materials. It fits the description perfectly.
• Carbon dioxide (CO₂): A colourless and odourless gas produced by the complete combustion of organic materials. It is not toxic in small concentrations but can be harmful in high concentrations.
• Nitrogen dioxide (NO₂): A reddish-brown gas with a characteristic sharp, biting odour. It is not colourless or odourless.