Of the common nuclear radiations listed, which type is most easily stopped by a short distance of air and has the least penetrating power?

Introduction / Context:
In nuclear chemistry and radiation physics, it is very important to compare the penetrating power of different types of radiation. This helps in planning shielding, safety measures and practical uses in medicine and industry. The classic radiations discussed are alpha, beta and gamma rays, alongside X rays. This question asks which of these is most easily stopped by air, meaning it has the lowest penetrating power and shortest range in air under normal conditions.

Given Data / Assumptions:

• The radiations considered are alpha rays, beta rays, gamma rays and X rays, with neutron radiation also listed as an option.
• We are concerned with how easily each radiation is stopped by a short distance of ordinary air.
• All radiations are assumed to have typical energies as found in common radioactive sources.
• No special shielding materials are considered, only air.

Concept / Approach:
Alpha particles are heavy, doubly positively charged helium nuclei. They interact strongly with matter and lose energy quickly, so they have a very short range in air, often only a few centimetres. Beta particles, which are electrons or positrons, are lighter and more penetrating than alpha particles but can still be stopped by a thin sheet of metal or a few millimetres of plastic. Gamma rays and X rays are high energy electromagnetic waves, far more penetrating and capable of passing through many centimetres of solid material. Neutrons can also penetrate deeply. Therefore, the radiation most easily stopped by air is alpha radiation.

Step-by-Step Solution:
Step 1: Recall that alpha particles are heavy helium nuclei with a +2 charge, giving them strong interactions with air molecules. Step 2: Because alpha particles lose energy rapidly, they travel only a few centimetres in air before being stopped. Step 3: Beta particles are lighter and interact less strongly, so they travel further in air than alpha particles and are not the easiest to stop. Step 4: Gamma rays and X rays are electromagnetic waves with high penetration, passing through air almost unhindered compared with alpha and beta particles. Step 5: Neutrons, although uncharged, can penetrate significant distances before being slowed and captured, so they are not easily stopped by air either. Step 6: Therefore, among the listed radiations, alpha rays are the ones most easily stopped by a short path of air.

Verification / Alternative check:
Practical demonstrations in physics laboratories show that alpha sources monitored with detectors lose almost all their radiation when a sheet of paper or a few centimetres of air are placed in the path. In contrast, beta radiation passes through paper and requires denser materials such as aluminium for effective shielding. Gamma rays and X rays demand thick lead or concrete for significant attenuation. Radiation protection guidelines consistently rank alpha as the least penetrating and gamma as the most penetrating. These observations support the conclusion that alpha rays are most easily stopped by air.

Why Other Options Are Wrong:
Option B, beta rays, are more penetrating than alpha rays and cannot be stopped as easily by air alone. Option C, gamma rays, have very high penetrating power and can travel long distances through air. Option D, X rays, are also electromagnetic waves with substantial penetration and require shielding for safety. Option E, neutron radiation, penetrates deeply into materials and is not easily stopped by air. Only option A correctly identifies alpha rays as the radiation type that is most easily stopped by air and has the shortest range.

Common Pitfalls:
A common misunderstanding is to assume that the radiation that is most dangerous at a distance must also be the hardest to stop. In reality, alpha radiation is extremely damaging if it gets inside the body, but it is very easy to stop externally. Another pitfall is mixing up energy with penetration; a lower energy gamma ray can still penetrate more than a higher energy alpha particle because of their different natures. Remember the simple ranking for penetrating power in air: alpha is least penetrating, followed by beta, with gamma and X rays being the most penetrating.

Final Answer:
The type of radiation most easily stopped by air is Alpha rays, which have very low penetrating power compared with beta, gamma, X rays and neutrons.