Overall the highest value of e/m ratio is for H+ ion.

Which gas has highest e by M ratio?

e/m ratio is observed in case of hydrogen gas. Reason : Hydrogen is the only element that does not carry any neutron. In anode ray discharge it carry 1 positive charge and mass is also 1.

For which of the following species e/m value is highest?

So, mass will be = . And, charge will be . Charge to mass ratio of helium is 0. Thus, we can conclude that hydrogen has maximum charge to mass ratio.