Question

Which gas on exposure to high concentrations can cause unconsciousness, known as "knockdown," which can be lethal?

• A. Hydrogen sulphide
• B. Galena
• C. carbon-monoxide
• D. none of these

Answer 1

The correct option is A Hydrogen sulphide

$H_{2}S$ being toxic causes a wide range of health hazards such as nausea, tearing of eyes, headache or loss of sleep or bronchial problems in some asthma patients; acute exposure causes rapid unconsciousness,' knockdown ' or immediate collapse, death within minutes.

Hence, option $A$ is correct.