There are two elementscalcium (atomic number 20) and argon (atomic number 18). The mass number of both the elements is 40. They are therefore known as

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Q: 16 (CDS-I/2017)
There are two elements—calcium (atomic number 20) and argon (atomic number 18). The mass number of both the elements is 40. They are therefore known as

question_subject: 

Logic/Reasoning

question_exam: 

CDS-I

stats: 

0,23,39,12,4,32,14

keywords: 

{'isotopes': [0, 0, 3, 6], 'atomic number': [0, 0, 0, 4], 'elements': [0, 0, 2, 5], 'isotones': [0, 0, 0, 2], 'mass number': [0, 0, 0, 3], 'isochores': [0, 0, 0, 1], 'isobars': [3, 1, 4, 4], 'calcium': [2, 0, 0, 4], 'argon': [2, 0, 3, 6]}

The correct answer is option 3: isobars.

Isobars are atoms that have the same mass number but different atomic numbers. In this question, both calcium and argon have a mass number of 40, indicating that they have the same total number of protons and neutrons in their nuclei. However, calcium has an atomic number of 20, while argon has an atomic number of 18. Atomic number represents the number of protons in an atom`s nucleus.

Isotones, option 1, are atoms that have the same number of neutrons but different number of protons and different mass numbers. Isochores, option 2, is not a valid term when referring to atoms.

Isotopes, option 4, are atoms that have the same number of protons but different numbers of neutrons. Isobars, option 3, is the correct term as they have the same mass number but different atomic numbers.