alleryThe atomic number Z of an element is defined as
ANumber of protons in the nucleus
BTotal number of protons + neutrons in the nucleus
CNumber of electrons in the outermost shell
DTotal mass of the atom in u
Answer & Solution
Correct answer: A. Number of protons in the nucleus
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: syllabus Chemistry, Ch 2 "Structure of Atom", §2.3_
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