Case: Read the passage and answer the question.
In science, there are notations and their interpretations. There is a notation to denote the nucleus of an atom in terms of its mass number A and atomic number Z. A lot of information about the nucleus and the atom can be drawn from it. Consider an element \( {}^{A}_{Z}\mathrm{X} \). Based on this information, answer the question that follows.
What is the charge on the nucleus?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → \( Ze \)
The nucleus of \( {}^{A}_{Z}\mathrm{X} \) contains \( Z \) protons, each carrying a charge \( +e \), and \( A-Z \) neutrons, which carry no charge.
The charge on the nucleus is:
\( \begin{aligned} q &= Z\times(+e)+(A-Z)\times0 \\ &= Ze \end{aligned} \)
This positive charge balances the charge \( -Ze \) of the \( Z \) electrons outside the nucleus, so the atom as a whole is neutral.
NCERT (2026-27):
Atomic Masses and Composition of Nucleus – “The positive charge in the nucleus is that of the protons. A proton carries one unit of fundamental charge and is stable. … The total charge of the atomic electrons is thus (–Ze), and since the atom is neutral, the charge of the nucleus is (+Ze).”