Explanation: In the Carbon-Nitrogen (CNO) cycle, carbon acts as a catalyst. The cycle involves nuclear fusion reactions in stars, where carbon is used in the reaction but is regenerated at the end, allowing it to continue facilitating the process without being consumed.

Explanation: Protons and neutrons, which are the particles found in the nucleus of an atom, are collectively referred to as nucleons.

Explanation: A telescope has a long tube and a large objective lens, designed for observing distant objects. In contrast, a microscope has a shorter tube and smaller objective lens, meant for viewing tiny objects up close. Telescopes provide higher magnification for faraway objects, while microscopes focus on fine details of small objects.

Explanation: X-rays can pass through calcium, but they are absorbed more than they pass through. This is because calcium has a higher atomic number than other elements, which means it has more electrons and interacts more with X-rays.

Explanation: Alpha rays are not electromagnetic in nature; they are a form of particulate radiation, consisting of helium nuclei (two protons and two neutrons). On the other hand, UV rays, gamma rays, and infrared rays are all forms of electromagnetic radiation.

Explanation: A Coolidge tube is used for generating X-rays, not microwaves. In contrast, devices like magnetrons, klystrons, and travelling wave tubes are used to generate microwaves.