Answer :
To analyze the statements about the isotopes of oxygen, we need to understand the definitions of mass number, atomic mass, atomic number, and what isotopes are.
- The mass number is the total number of protons and neutrons in the nucleus of an atom.
- The atomic mass is the weighted average mass of all the isotopes of an element.
- The atomic number is the number of protons in the nucleus of an atom and defines the element.
- Isotopes are variants of a particular chemical element which differ in neutron number, while all isotopes of a given element have the same number of protons.
Given this information, let's analyze the statements:
a. All of the isotopes have eight neutrons.
This statement is false. While it's true that the most common isotope of oxygen has 8 neutrons (oxygen-16, with a mass number of 16 and an atomic number of 8, meaning 16 - 8 = 8 neutrons), oxygen can have different isotopes with more or fewer neutrons, such as oxygen-17 with 9 neutrons and oxygen-18 with 10 neutrons.
b. All of the isotopes have eight neutrons or more.
This statement is true. The atomic number of oxygen is 8, which means there are always 8 protons in the nucleus. The mass number must be greater than or equal to the atomic number (since it is the sum of protons and neutrons), which means there cannot be fewer than 8 neutrons. Therefore, all isotopes of oxygen have at least 8 neutrons.
c. Some of the isotopes have fewer than eight neutrons.
This statement is false. As explained above, since the atomic number of oxygen is 8, and the atomic number dictates the number of protons, you cannot have an isotope of oxygen with fewer than 8 neutrons. This would result in a mass number that is less than the atomic number, which is not possible.
d. All of the isotopes have fewer than eight neutrons.
This statement is false for the same reason as statement c. You cannot have an isotope of oxygen with fewer than 8 neutrons because it would imply that there are fewer nucleons (protons and neutrons) than there are protons, which is not possible.
Hence, the correct answer is:
b. All of the isotopes have eight neutrons or more.
