Which of the following statements correctly describes alpha particles in the context of radioactivity?

Introduction / Context:
This question belongs to nuclear chemistry and radioactivity. Alpha particles are one of the three main types of nuclear radiation, along with beta particles and gamma rays. Understanding what alpha particles physically are helps explain their charge, mass, ionizing power and penetration ability. The question asks which statement correctly describes alpha particles, so you must pick the statement that matches their true nature.

Given Data / Assumptions:

• Alpha particles are emitted in some radioactive decays.
• Options describe their mass, charge, relation to helium nuclei, ionizing power and masslessness.
• We assume standard textbook definitions.

Concept / Approach:
An alpha particle consists of two protons and two neutrons bound together, which is exactly the composition of the nucleus of a helium atom. Therefore, an alpha particle is essentially a helium nucleus with a charge of plus two and a relatively large mass compared to electrons and beta particles. It is positively charged, strongly ionizing, and has low penetration power compared to beta and gamma radiation. Any statement that describes alpha particles as negatively charged, massless or less ionizing than gamma rays is incorrect.

Step-by-Step Solution:
Step 1: Recall that alpha decay occurs when an unstable nucleus emits an alpha particle of two protons and two neutrons. Step 2: The nucleus of a helium atom, also called a helium 4 nucleus, consists of two protons and two neutrons, which matches the composition of an alpha particle. Step 3: Therefore, the statement that alpha particles are just like helium nuclei is correct. Step 4: Examine option A, claiming alpha particles have about twice the mass of beta particles. In reality, an alpha particle is much more massive than a beta particle, which is essentially an electron or positron. The mass difference is far more than a factor of two, so this description is misleading. Step 5: Option B states that alpha particles are negatively charged, which is false; they carry a charge of plus two because of their two protons and no electrons. Step 6: Option D claims they have lower ionizing power than gamma rays, which is the opposite of what is true. Alpha particles are strongly ionizing but have low penetration, while gamma rays are weakly ionizing but highly penetrating. Step 7: Option E describes them as massless neutral particles, which would be closer to photons or neutrinos, not alpha particles. Step 8: Therefore, the only correct description is that alpha particles are just like helium nuclei.

Verification / Alternative check:
Nuclear equations reinforce this view. For example, when uranium 238 decays to thorium 234, it emits an alpha particle written as 4 2 He, clearly representing a helium nucleus. The notation with mass number 4 and atomic number 2 is standard and directly links alpha particles with helium nuclei. This is widely taught in nuclear chemistry and physics, confirming that identifying alpha particles as helium nuclei is correct.

Why Other Options Are Wrong:
Alpha particles are not slightly heavier than beta particles; they are thousands of times more massive because beta particles are essentially electrons. They are positively charged, not negatively charged. Their ionizing power is higher, not lower, than that of gamma rays. They certainly are not massless neutral particles like photons. These incorrect descriptions conflict with experimental evidence and standard teaching on radioactivity.

Common Pitfalls:
Students may misremember the comparison of ionizing and penetrating power of the three types of radiation. A useful rule is that alpha particles are highly ionizing but weakly penetrating (stopped by paper), beta particles have moderate ionizing and penetrating power, and gamma rays are weakly ionizing but highly penetrating. Mixing up these trends can lead to wrong choices in questions like this. Keeping the helium nucleus image in mind helps fix the properties of alpha particles more securely.

Final Answer:
Alpha particles are correctly described as just like helium nuclei composed of two protons and two neutrons.