International Electrotechnical Commission (IEC) which was first formed in 1906 is the predominant organization for developing and publishing international standards for technologies related to electrical and electronic devices and processes. The standards developed by this association are widely used in scientific fields such as power generation, semiconductors, fibre optics, batteries, solar energy, nanotechnology and marine energy. They also proposed the International System of Units( SI unit) used in many fields of study today.
The atomic number is the number of protons. So, you can subtract the atomic number from the mass number to find the number of neutrons. I hope this helps! :)
