All large radioactive atoms decay into smaller atoms by releasing alpha particles. Each alpha particle has 2 protons, 2 neutrons, and 0 electrons. The table below describes several neutral, low-mass atoms.

\begin{tabular}{|l|l|l|l|}
\hline \multicolumn{4}{|c|}{Stable Isotopes of Low-Mass Elements} \\
\hline Element Name & Symbol & \begin{tabular}{l} Atomic \\ Number \end{tabular} & \begin{tabular}{l} Number of \\ Neutrons \end{tabular} \\
\hline Hydrogen & H & 1 & 0 \\
\hline Helium & He & 2 & 2 \\
\hline Lithium & Li & 3 & 4 \\
\hline Beryllium & Be & 4 & 5 \\
\hline
\end{tabular}

An alpha particle is also referred to as a nucleus of which isotope?

A. lithium-7
B. helium-4
C. hydrogen-2
D. helium-2



Answer :

Given the properties described in the question, let's analyze each step carefully to determine which isotope corresponds to an alpha particle.

1. Understanding Alpha Particles:
- Each alpha particle comprises 2 protons and 2 neutrons.
- This makes the total mass number of an alpha particle [tex]\(2 + 2 = 4\)[/tex].

2. Isotopic Notation:
- An isotope is often represented as [tex]\(\text{Element-Symbol (total number of protons + neutrons)}\)[/tex].

3. Evaluating Each Option:
- Lithium-7:
- Lithium (Li) has an atomic number of 3 (3 protons).
- This isotope is [tex]\( \text{Li-7} \)[/tex], meaning it has 7 - 3 = 4 neutrons.
- So it has 3 protons and 4 neutrons, which does not match an alpha particle (2 protons and 2 neutrons).

- Helium-4:
- Helium (He) has an atomic number of 2 (2 protons).
- This isotope is [tex]\( \text{He-4} \)[/tex], meaning it has 4 - 2 = 2 neutrons.
- So it has 2 protons and 2 neutrons, which matches an alpha particle exactly.

- Hydrogen-2:
- Hydrogen (H) has an atomic number of 1 (1 proton).
- This isotope is [tex]\( \text{H-2} \)[/tex], meaning it has 2 - 1 = 1 neutron.
- So it has 1 proton and 1 neutron, which does not match an alpha particle.

- Helium-2:
- Helium (He) has an atomic number of 2 (2 protons).
- This isotope is [tex]\( \text{He-2} \)[/tex], meaning it has 2 - 2 = 0 neutrons.
- So it has 2 protons and 0 neutrons, which does not match an alpha particle.

4. Conclusion:
- Among the given options, the isotope that matches the properties of an alpha particle (2 protons and 2 neutrons) is helium-4.

The correct answer is: helium-4.

So, an alpha particle is also referred to as the nucleus of helium-4.

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