An atom of element Be has four protons, four electrons, and five neutrons. Which element below could be an isotope of this atom? Sodium-10, beryllium-10, boron-9, carbon-9.
The Correct Answer and Explanation is:
The correct answer is beryllium-10.
Explanation:
An isotope is defined as an atom of the same element that has the same number of protons but a different number of neutrons. The atomic number (which is the number of protons) identifies the element, while the mass number is the sum of protons and neutrons.
Let us analyze the given atom:
- The atom has 4 protons, which means it is beryllium (Be) since the atomic number of beryllium is 4.
- It has 4 electrons, which means the atom is electrically neutral.
- It has 5 neutrons.
The mass number is calculated as:Mass number=Number of protons+Number of neutrons=4+5=9\text{Mass number} = \text{Number of protons} + \text{Number of neutrons} = 4 + 5 = 9Mass number=Number of protons+Number of neutrons=4+5=9
Thus, this atom is beryllium-9, the most common isotope of beryllium.
Now, let us check the options to find an isotope:
- Sodium-10: Sodium has an atomic number of 11, so it has 11 protons. It is a different element, not an isotope of beryllium.
- Beryllium-10: This is still beryllium, meaning it has 4 protons but a different number of neutrons. Specifically, beryllium-10 has 6 neutrons. Since isotopes only differ in neutron number, beryllium-10 is an isotope of beryllium-9.
- Boron-9: Boron has 5 protons, so it is a different element, not an isotope of beryllium.
- Carbon-9: Carbon has 6 protons, so it is a different element, not an isotope of beryllium.
Conclusion:
Only beryllium-10 has the same number of protons as the given atom but a different mass number due to a different number of neutrons, making it an isotope of the given beryllium atom.
