Gases can be chemically active or inactive. This means that a gas either reacts or does not react when combined with other elements.
A definition of a noble gas is a gas that does not combine easily with other elements. An example of a noble gas is helium. A protective layer of helium prevents reactions with other elements such as oxygen.
Helium has a very low density. It is used daily in weather balloons to carry instruments that record temperature, humidity, and pressure readings in the atmosphere.
People with breathing problems may be treated with a mixture of helium and oxygen. Helium atoms are small and light. A helium-oxygen mixture can be pumped in and out of the lungs more easily than air. Helium-oxygen mixtures are also used in breathing tanks of deep-sea divers.

Using information from the passage, which statement is accurate?

1.A noble gas mixes well with other elements.
2.Gases usually are chemically active.
3.Helium is an example of a chemically inactive gas.
4.Helium-oxygen mixtures are used in weather balloons.