The atomic number Z of an element is defined as
A{'text': 'Number of protons in the nucleus', 'label': 'A'}
B{'text': 'Total number of protons + neutrons in the nucleus', 'label': 'B'}
C{'text': 'Number of electrons in the outermost shell', 'label': 'C'}
D{'text': 'Total mass of the atom in u', 'label': 'D'}
Answer & Solution
Correct answer: A. {'text': 'Number of protons in the nucleus', 'label': 'A'}
1. Atomic number Z is a defining property of an element.
2. Z equals the number of protons in the nucleus of the atom.
3. In a neutral atom, Z also equals the number of electrons.
4. Mass number A = protons + neutrons; A − Z = neutron count.
_Source: NCERT Class 11 Chemistry, Ch 2 "Structure of Atom", §2.3_
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