The correct answer is A. Chlorine.
Chlorine is a chemical element with the symbol Cl and atomic number 17. It is a pale yellow-green gas at standard temperature and pressure and exists as a diatomic molecule. It is an extremely reactive element and is a member of the halogen group in the periodic table. Chlorine is used in a wide variety of applications, including the production of bleach, PVC, and other chemicals.
Radon is a chemical element with the symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless noble gas that occurs naturally in the Earth’s atmosphere. Radon is a decay product of uranium and thorium, and it is found in uranium ore and in rocks that contain uranium. Radon can also be found in soil and water. Radon is a health hazard because it can cause lung cancer.
Krypton is a chemical element with the symbol Kr and atomic number 36. It is a noble gas that is colorless, odorless, and tasteless. Krypton is found in the Earth’s atmosphere in very small amounts. It is also found in natural gas and in some minerals. Krypton is used in a variety of applications, including lighting, lasers, and electronics.
Helium is a chemical element with the symbol He and atomic number 2. It is a noble gas that is colorless, odorless, and tasteless. Helium is the second most abundant element in the universe, after hydrogen. It is found in the Earth’s atmosphere in very small amounts. It is also found in natural gas and in some minerals. Helium is used in a variety of applications, including balloons, cryogenics, and rocketry.