The maximum e/m ratio for positive rays is obtained when they discharge tube contains:

Explanation

Option D is correct. The maximum e/m ratio for positive rays is achieved with H2 because it is the lightest atom, resulting in the highest charge-to-mass ratio. The e/m ratio is defined as the charge of a particle divided by its mass, and it indicates how much a particle is influenced by electric and magnetic fields. A higher e/m ratio means greater deflection in these fields. The other options (He, N2, and Ne) are heavier than hydrogen, which results in lower e/m ratios due to their greater mass. Understanding the e/m ratio is crucial in identifying elements in gases and was pivotal in early atomic research, such as J.J. Thomson's work on the electron's mass.