The gas that is required to allow rusting to occur is Oxygen
Helium gas
bcoz oxygen is used by living beings were nitrogen is not used.
oxygen
Eudiometer is an instrument which measure the change in the volume of gas (or mixture of gases) as a consequence of chemical or physical processes.
The gas that is required to allow rusting to occur is Oxygen
the manometer is frequently used
an instrument that is used to measure gas in a closed container. A+
A manometer is an instrument that can be used to measure the pressure in an enclosed container that is filled with gas. The manometer is sometimes called a pressure gauge.
You would measure O2 since the plants give off oxygen. O2 is Oxygen gas.
Carbon dioxide is the gas that should be used to measure the rate of photosynthesis. The resultant gas which is oxygen can also be used to tell us the rate of photosynthesis.
A=Spirometer(Answered by Teshome Seya)*source-Tbar's medical dictionary.A spirometer is a device that measures the volume of air inhaled and exhaled by the lungs.A spirometer is used to measure breathing.Spirometerspirometeryou donta stethascope. 
Paramagnetic Oxygen Analyzer is used to measure the content of oxygen not only in flammable gas mixtures but also in low concentrations, with high precision.
A flowmeter is an instrument that is used to designed the rate of flow for a liquid or a substance such as a gas. The measure of the substance is by the volume of its weight. A flow meter can measure many substances that otherwise would not be measurable.
An anemometer is a device used to measure the speed of wind. It also can be used to measure the current within a gas.
Helium gas
bcoz oxygen is used by living beings were nitrogen is not used.