Calcium has 20 electrons and 20 neutrons and Argon has 18 protons and 22 neutrons. What is similar between them?

Calcium has 20 electrons and 20 neutrons and Argon has 18 protons and 22 neutrons. What is similar between them? Correct Answer Mass number

The correct answer is Mass number.

Key Points

• The mass number of both Calcium and Argon is 40.
• Calcium and Argon are isobars, as both have the same mass number and different atomic numbers. 
  • It indicates the same number of nucleons i.e. total number of neutrons and protons in the nucleus.
  • The total number of protons and neutrons in calcium is 20 + 20 = 40.
  • The total number of neutrons and protons in Argon is 18 + 22 = 40.
  • Hence, the mass number of both the elements is 40.

Hence, the similarity between the two elements is that they have the same mass number.

Additional Information

• As the atomic number of calcium is 20 it indicates the number of protons are 20 and the atomic number of argon is 18 so the number of protons are 18.

• Such an element whose atomic numbers are different but the mass number is the same are called isobar.
• Such elements whose atomic numbers are the same but atomic mass differs are called isotopes.
• Hydrogen has three isotopes - Protium, Deuterium, and Tritium.