He-Ne laser utilizesa.Optical pumpingb.Electrical discharge and atom-atom collisionc.Electrical discharge

The He-Ne (Helium-Neon) laser utilizes electrical discharge and atom-atom collision. Here's a step-by-step explanation:

1. Electrical Discharge: A high voltage is applied to the He-Ne gas mixture. This causes the electrons to gain energy and move to a higher energy level.

2. Atom-Atom Collision: The excited electrons in the helium atoms collide with the neon atoms. This transfers the energy from the helium to the neon, causing the neon atoms to move to a higher energy level.

3. Light Emission: The excited neon atoms then return to their ground state by emitting a photon of light. This light is the laser light that we see.

So, the correct answer is b. Electrical discharge and atom-atom collision.