Which property of the nitrogen cycle makes it a good illustration of the conservation of matter?

In the process of the nitrogen cycle.                 
The nitrogen cycle is a biogeochemical succession process of nitrogen that involves: fixation, ammonification, nitrification, and denitrification. Like any other biogeochemical cycles. This process undergoes and affects the biological, geometrical and chemical aspects in the ecosystem and the abiotic and biotic community. Hence, the nitrogen cycle leads the abiotic component –nitrogen- to contribute to the biotic community, decomposition and primal production. Further, it becomes an essential part of the environment because some life components are contains it, similarly, amino acids, nucleic acids in RNA and DNA.  

answer: carbon 14 can only be used to determine the age of the organisms that were once living, and igneous rocks are non living.

explanation:

carbon 14 dating is used to determine the age of the sample by estimating the amount of carbon 14 present in the sample and then comparing it with a reference standard.carbon 14 is a isotope of carbon which is radioactive and unstable. carbon 14 is assimilated by all plants and animals throughout their life from carbon dioxide. however, one the organisms die they stop this assimilation and the carbon 14 content starts to decrease.by knowing how much of carbon 14 is left in an organism after his death, one can estimate the age of the organism. the materials whose age can be estimated by carbon 14 method are the organic compounds. however, some inorganic compounds such as aragonite   shell can also be dated.however, if we consider the igneous rocks it is a non living component which never accumulated carbon 14 in it and thus, we cannot use carbon 14 dating method to estimate its age.