MCQ practice · SSC Chemistry Board questions · Chapter 3: Structure of Matter
Which element has equal numbers of electrons, protons and neutrons?
Think it through first, then pick an option.
- a Na
- b K
- c Ca
- d Cl
Answer and explanation
Correct answer: c Ca
⁴⁰₂₀Ca has 20 electrons, 20 protons and 20 neutrons.
Why the other options are wrong
- a Na: Sodium has more neutrons (12) than protons (11); calcium is the one with all equal.
- b K: ³⁹₁₉K has 19 protons and 20 neutrons; not equal.
- d Cl: ³⁵₁₇Cl has 17 protons and 18 neutrons; not equal.
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