Understanding Isotopes and Isobars Pairs

This question asks us to identify the correct relationship between atomic properties for isotopes and isobars. Let's break down the definitions of these terms.

Defining Isotopes

Isotopes are atoms of the same element. This means they must have the same number of protons, which defines the atomic number ($Z$). However, isotopes differ in the number of neutrons ($N$) in their nucleus. Since the mass number ($A$) is the sum of protons and neutrons ($A = Z + N$), having a different number of neutrons leads to different mass numbers.

• Same Atomic Number ($Z$)
• Different Number of Neutrons ($N$)
• Therefore, Different Mass Numbers ($A$)

Statement I says: "Isotopes – different mass numbers". Based on our definition, this statement is correct because isotopes have the same atomic number but varying numbers of neutrons, resulting in different mass numbers.

Defining Isobars

Isobars, on the other hand, are atoms that belong to different elements. This means they have different numbers of protons and thus different atomic numbers ($Z$). However, isobars are characterized by having the same mass number ($A$). This occurs when atoms with different numbers of protons also have different numbers of neutrons such that their total mass number ($A = Z + N$) remains the same.

• Different Atomic Numbers ($Z$)
• Different Number of Neutrons ($N$)
• Same Mass Number ($A$)

Statement II says: "Isobars – different atomic numbers". Since isobars are atoms of different elements, they must have different numbers of protons, meaning they have different atomic numbers. Therefore, this statement is also correct.

Conclusion on Correct Pairs

We've established that:

• Statement I is correct: Isotopes have different mass numbers.
• Statement II is correct: Isobars have different atomic numbers.

Since both statements accurately describe the properties of isotopes and isobars respectively, the correct option includes both I and II.