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Q12
(NDA-I/2022)
Science & Technology › Basic Science (Physics, Chemistry, Biology) › Atomic and nuclear physics
Answer Verified
The mass number of argon is 40. Which one of the following statements is correct?
Result
Your answer:
—
·
Correct:
C
Explanation
Argon (Ar) is a noble gas with an atomic number of 18. The atomic number represents the number of protons in the nucleus of an atom [1]. In a neutral atom, the number of electrons is equal to the number of protons to maintain electrical neutrality [1]. Therefore, an argon atom contains 18 protons and 18 electrons. The mass number is defined as the sum of protons and neutrons [1]. Given a mass number of 40 for argon, the number of neutrons is calculated as 40 minus 18, which equals 22 neutrons. Consequently, statement 1 is incorrect (18 protons, not 22), statement 2 is incorrect (22 neutrons, not 18), and statement 4 is incorrect (sum of protons and electrons is 36, not 40). Statement 3 is correct as argon has 18 electrons.
Sources
- [1] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > 3.3 HOW DO METALS AND NON-METALS REA ALS REACT? > p. 47
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