Atomic Structure
ID: #2022 | Difficulty: easy
AI Quick Answer:
The correct option for this defence exam question is (A) which is 41. Detailed proof and explanation are supplied below.
An isotope of an element has an atomic number of 37 and a mass number of 78. What is the number of neutrons in its nucleus?
Key Takeaways for NDA & CDS Candidates
- Ensure you recall the standard formulas for Atomic Structure during UPSC exam preparation.
- Eliminating obviously incorrect choices based on dimensional analysis or limits saves valuable seconds.
- Expert tip: Written defence mock tests should be practiced weekly with strict negative marking rules.
Correct Answer: (A)
41
Step-by-Step Explanation
The mass number (A) of an atom is the sum of the atomic number (Z, which represents protons) and the number of neutrons (N).
Formula: Mass Number (A) = Protons (Z) + Neutrons (N)
Therefore, Neutrons (N) = Mass Number (A) - Atomic Number (Z)
Given:
Z = 37
A = 78
N = 78 - 37 = 41 neutrons.
Formula: Mass Number (A) = Protons (Z) + Neutrons (N)
Therefore, Neutrons (N) = Mass Number (A) - Atomic Number (Z)
Given:
Z = 37
A = 78
N = 78 - 37 = 41 neutrons.
| Question Metadata Summary | |
|---|---|
| Exam Category | UPSC NDA / CDS / AFCAT / Agniveer |
| Subject Unit | NDA Chemistry Questions |
| Sub-topic / Module | Atomic Structure |
| Correct Option | Option (A) |
| Target Year | UPSC Defence Exams 2026 |