Which of the following pairs represents isobars?

The correct answer is 40K19 and 40Ca20Key Points

• Isobars are atoms of different elements that have the same mass number but different atomic numbers.
• The given pair 40K19 and 40Ca20 are isobars because their mass number is the same (40) but their atomic numbers differ (19 and 20, respectively).
• While both have the same number of nucleons (protons + neutrons), their chemical properties differ due to different atomic numbers.
• Option 1, 40K19 and 39K19, cannot be isobars as they belong to the same element (potassium) and differ in mass number, making them isotopes instead.
• Similarly, options like 3He2 and 4He2 or 24Mg12 and 25Mg12 are isotopes, not isobars, as they represent the same element with varying mass numbers.

Additional Information

• Mass Number (A): The total number of protons and neutrons in an atom's nucleus. It determines the mass of the atom.
• Atomic Number (Z): The number of protons in the nucleus of an atom, which defines the element's identity and its position in the periodic table.
• Isotopes: Atoms of the same element that have the same atomic number but different mass numbers due to a varying number of neutrons. Example: ¹²C₆ and ¹⁴C₆.
• Isobars: Atoms of different elements with the same mass number but different atomic numbers. Example: 40K19 and 40Ca20.
• Applications of Isobars: Isobars like ¹⁴C₆ (Carbon-14) are used in radiocarbon dating, while others are employed in medical imaging and nuclear medicine.