(d) Nitrogen
Nitrogen is a colorless and odorless gas that occupies 78.1% of the atmosphere (volume ratio). It is produced in large quantities together with oxygen (bp -183.0 oC) by liquefying air (bp -194.1 oC) and fractionating nitrogen (bp -195.8 oC). Nitrogen is an inert gas at room temperatures but converted into nitrogen compounds by biological nitrogen fixation and industrial ammonia synthesis. The cause of its inertness is the large bond energy of the NN triple bond.
The two isotopes of nitrogen are 14N (99.634%) and 15N (0.366%). Both isotopes are NMR-active nuclides.