A particle which is four times the mass and two times the charge of a proton is known as what?

Introduction / Context:
Nuclear physics deals with subatomic particles such as protons, neutrons, and composite nuclei. Some radioactive elements emit characteristic particles, and understanding their mass and charge is important for identifying them. This question asks you to recognise a particle whose mass and charge are related in a specific way to a proton, a basic building block of the nucleus.

Given Data / Assumptions:

• We compare the unknown particle to a proton.
• Its mass is four times the mass of a proton.
• Its charge is two times the charge of a proton.
• Options include helium atom, alpha particle, deuteron, tritium nucleus, and a proton pair.
• We assume knowledge of common nuclear particles.

Concept / Approach:
A proton has a charge of plus one elementary unit and a mass approximately equal to one atomic mass unit. An alpha particle is the nucleus of a helium 4 atom and consists of two protons and two neutrons. This gives it a charge of plus two and a mass about four times that of a proton. A helium atom is neutral and includes electrons, while a deuteron is the nucleus of hydrogen 2 with mass roughly two and charge plus one. Tritium has even higher mass. Therefore, the description of four times mass and twice charge matches an alpha particle.

Step-by-Step Solution:
Step 1: Recall that a proton has mass about one atomic mass unit and charge plus one. Step 2: The unknown particle is said to have four times the mass of a proton, so its mass is about four atomic mass units. Step 3: The particle has a charge twice that of a proton, meaning charge plus two. Step 4: An alpha particle is the nucleus of a helium 4 atom, containing two protons and two neutrons, which gives mass about four units and net charge plus two. Step 5: A helium atom includes two electrons and is charge neutral, so it does not match the given charge description. Step 6: Deuterons and tritium nuclei have different mass and charge combinations, so they do not fit the given conditions. Thus, the particle is an alpha particle.

Verification / Alternative check:
Radioactive decay of heavy nuclei like uranium often emits alpha particles. Data tables for alpha radiation list charge plus two and mass equal to four atomic mass units. This exactly agrees with the relationship to a proton given in the question. Considering how an alpha particle is built from two protons and two neutrons also helps: protons contribute to both mass and charge, while neutrons add mass without charge, giving the observed ratio of mass and charge compared to a single proton.

Why Other Options Are Wrong:
Helium atom: It has two protons and two electrons, so it is electrically neutral, not charged plus two.
Deuteron: Nucleus of heavy hydrogen with one proton and one neutron, mass about two units and charge plus one, not four and plus two.
Tritium nucleus: Has one proton and two neutrons, mass about three units and charge plus one, again not matching the given values.
A pair of protons loosely bound: Two protons would have charge plus two but mass about two units, not four, and do not form a stable nucleus by themselves without neutrons.

Common Pitfalls:
A frequent mistake is to confuse a helium atom with a helium nucleus. The atom includes electrons and can be neutral, while the alpha particle is positively charged. Another pitfall is to focus only on mass or only on charge; the question specifies both four times mass and two times charge, and the correct answer must satisfy both conditions. Always check all given properties against each option before deciding.

Final Answer:
A particle with four times the mass and two times the charge of a proton is an alpha particle, which is the nucleus of helium 4.