Electrical breakdown in a mixed gas is investigated. The plasma at breakdown
is evaluated in terms of the mole fraction χ. The optimum condition for the
highest plasma density is described in terms of the ionization energy and collisional
cross-section of the mixed gas. The optimum mole fraction for the highest plasma
density is found to be χ = 0.03 for the case of plasma generation in neon gas mixed
with xenon for a plasma display panel. The optimum condition for the highest
number of electronic excitations is also obtained.