Question

which of the following is always the same for multiple isotopes of a single element? a. atomic number b. atomic mass number c. tendency to decay radioactively d. none of the above are correct.

Answer 1

a. atomic number

Step-by-step explanation:

You want to know which is the same for multiple isotopes of an element:

• atomic number
• atomic mass number
• tendency to decay
• none of the above

Atomic Number

The atomic number identifies the element. It is the number of protons in the nucleus. The atomic number is always the same for different isotopes of an element. (Choice A)

Atomic Mass Number

The atomic mass number is the total number of protons and neutrons in the nucleus of an element. It is used to identify the isotope. Some isotopes of an element may be radioactive, and some may not be. Obviously, the atomic mass number is different for different isotopes.

For example, Oxygen has an atomic number of 8. There are isotopes of oxygen ranging from O-11 to O-26, most of which are radioactive. The one with the longest half-life is O-15, about 122 seconds. There are three stable isotopes, O-16, O-17, and O-18, with O-16 being by far the most abundant. About 0.2% of oxygen is O-18, and about 0.04% is O-17.

Different elements may have isotopes with the same atomic mass number. Such elements are called isobars. An example is Na-24 with an atomic number of 11, and Mg-24 with an atomic number of 12.