atom structure

[rituparna]

why does the e/m ratio of protons changes from gas to gas

[rktpro]

Do you deliberately mean 'protons' rather proton. I don't think literature ever mentions charge by mass ratio of system of particles.

Even then:No e\m doesn't change. It is constant.

[swansont]

e/m only makes sense for a bare particle. Once it's bound, the mass of the system changes (it has to release energy to become bound, so the mass changes), so it's going to vary from atom to atom, and you can't really assign the mass change to one particle in the atom. Which kinda makes it a meaningless measurement.

[Enthalpy]

rituparna, did you really mean e/m for protons, or for ions? For ions it would depend on the proportion of neutrons versus protons.