The correct answer is C. Only 3.
Carbon dioxide (CO2) is a colorless, odorless gas that is slightly heavier than air. It is a major component of the Earth’s atmosphere, and it is also found in volcanic gases, soda water, and carbonated beverages.
CO2 is not a poisonous gas. In fact, it is essential for life on Earth. Plants use CO2 to produce food through photosynthesis. Humans and other animals exhale CO2 as a waste product.
CO2 is an acidic oxide. This means that it reacts with water to form carbonic acid. Carbonic acid is a weak acid, but it can cause some materials to corrode.
CO2 does turn lime water milky. Lime water is a solution of calcium hydroxide. When CO2 is added to lime water, it reacts with the calcium hydroxide to form calcium carbonate. Calcium carbonate is a white solid, which is what causes the lime water to turn milky.
Therefore, only statement 3 is correct.