Nitrogen in a carbon dioxide laser isa.Used as a coolantb.Not used in this laserc.Used to induce excitation of another atom

The correct answer is c. Nitrogen is used to induce excitation of another atom in a carbon dioxide laser. Here's a step-by-step explanation:

1. In a carbon dioxide laser, a mixture of gases is used, typically consisting of carbon dioxide (CO2), helium (He), and nitrogen (N2).

2. The laser action in a CO2 laser starts with the excitation of nitrogen molecules by an electric discharge.

3. The excited nitrogen molecules then collide with CO2 molecules. During this collision, the energy is transferred from the nitrogen molecules to the CO2 molecules, causing them to get excited.

4. The excited CO2 molecules then emit light (laser) when they return to their ground state.

5. The role of helium in this process is to remove the heat and bring the CO2 molecules back to their lower energy state, so they can be excited again.

So, nitrogen is not used as a coolant (that's the role of helium), and it is definitely used in a CO2 laser (contrary to option b). Its role is to induce excitation of the CO2 molecules, which is why option c is the correct answer.