The correct answer is option 1 - Sulphur dioxide.

Sulphur dioxide (SO2) is a highly toxic gas that is released from burning fossil fuels, such as coal and oil, and industrial processes. It is known to cause severe health hazards, especially to the respiratory system. When inhaled, sulphur dioxide can irritate the airways, leading to symptoms like coughing, wheezing, and shortness of breath. Prolonged exposure to high levels of sulphur dioxide can cause chronic respiratory problems and may worsen existing respiratory conditions, such as asthma and bronchitis.

While carbon monoxide, ozone, and nitrogen oxide are also air pollutants that can have negative health effects, sulphur dioxide is considered the most serious pollutant due to its strong toxic properties and significant impact on the respiratory system.