Correct Answer: Helium

Solution : The correct option is Helium.

Helium is a common gas used to fill weather balloons. Because helium is lighter than air, it provides the buoyancy required to lift the weather balloon into the atmosphere. The gas provides the buoyancy required to transport equipment and sensors into the upper atmosphere in order to gather data on temperature, humidity, pressure, and other atmospheric parameters. Hydrogen was once frequently used for filling weather balloons, but due to its flammability, helium has become a safer and more regularly utilised alternative.