The correct answer is A. Ammonia.
Ammonia is a gas that is lighter than air and has a strong odor. It is used in many household products, such as cleaners and fertilizers. When ammonia is dissolved in water, it forms ammonium hydroxide, which is a base. Bases are substances that can neutralize acids. When an acid and a base are mixed, they react to form a salt and water.
Sulphur dioxide is a gas that is heavier than air and has a sharp odor. It is produced when fossil fuels are burned. Sulphur dioxide is a pollutant that can cause acid rain.
Hydrogen is a gas that is lighter than air and has no odor. It is the most abundant element in the universe. Hydrogen is used in many industrial processes, such as the production of ammonia.
Carbon dioxide is a gas that is heavier than air and has a slightly acidic odor. It is produced when organic matter is burned. Carbon dioxide is a greenhouse gas that contributes to climate change.
In conclusion, the gas dissolved in water that makes it basic is ammonia. Ammonia is a gas that is lighter than air and has a strong odor. It is used in many household products, such as cleaners and fertilizers. When ammonia is dissolved in water, it forms ammonium hydroxide, which is a base. Bases are substances that can neutralize acids.