1. The problem statement, all variables and given/known data When a gas is enclosed in an impermeable box and heated to a high temperature T, some of the neutral atoms lose an electron and become ions. If the number density of neutral atoms, ions and electrons is Na , N i and N e , respectively, these can be related to the average volume V a occupied by an atom/ion and the ionisation energy E by the relation 2. Options (a) N e (N a + N i ) = (N a /V a ) exp (−E/k B T ) (b) N a (N e + N i ) = (N a /V a ) exp (−E/k B T ) (c) N e N i = (N a /V a ) exp (+E/k B T ) (d) N e N i = (N a /V a ) exp (−E/k B T ) 3. The attempt at a solution The Maxwell distribution is Ne=Ngexp(-E/kBT). Where Ng and Ne are number of atoms in ground state and exited state respectively, E is the energy difference between the states. I don't know how to apply this concept here and how the average volume occupied by atom, Va enters the equation. Please give me hints to solve this problem. Problem Reference: TIFR GS 2012 Physical Sciences Question Paper.