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Question

If \(x\) is the number of electrons and \(y\) is the number of nucleons present in \({}_{16}^{32}S^{2-}\), then which one of the following is correct?

This question was previously asked in
NDA 2 2026 GAT Question Paper (13-Sep-2026)
The correct answer is
\(x = 18\) and \(y = 32\)

Calculating Electrons and Nucleons in \({}_{16}^{32}S^{2-}\) Ion

To determine the number of electrons (\(x\)) and nucleons (\(y\)) in the given sulfur ion, \({}_{16}^{32}S^{2-}\), we need to interpret the notation.

Understanding the Notation \({}_{Z}^{A}X^{charge}\)

  • The subscript \(Z\) represents the atomic number (number of protons).
  • The superscript \(A\) represents the mass number (total number of nucleons: protons + neutrons).
  • The chemical symbol \(X\) represents the element.
  • The superscript indicating the charge shows the net charge of the ion.

Determining the Number of Nucleons (\(y\))

The number of nucleons is the mass number (\(A\)). In \({}_{16}^{32}S^{2-}\), the mass number \(A\) is 32.

Therefore, \(y = 32\).

Determining the Number of Electrons (\(x\))

The atomic number \(Z\) is 16, which means a neutral sulfur atom has 16 protons and 16 electrons.

The ion has a charge of \(2-\). This indicates that the atom has gained 2 electrons compared to the neutral state.

Number of electrons (\(x\)) = Number of protons + Charge magnitude

Number of electrons (\(x\)) = \(16 + 2 = 18\).

Conclusion

Based on the calculations:

  • Number of electrons (\(x\)) = 18
  • Number of nucleons (\(y\)) = 32

This corresponds to the option where \(x = 18\) and \(y = 32\).

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Important Questions from Atomic Structure

  1. An element with atomic number 103 has a nuclear charge of +103. So its charge would be balanced by ________.

  2. An electron near the nucleus is strongly attracted by the nucleus and has _________.

  3. How many emission spectrum for sodiumlie in the range 588 - 590 nm?

  4. What is the atomic number of Bohrium which is named after physicist Niels Bohr, one of the founders of quantum theory?

  5. The quantum numbers n and l for four electrons are given below.

    (i) n = 4, I = 1

    (ii) n = 4, l = 0

    (iii) n = 3, l = 2

    (iv) n = 3, l = 1

    The order of their energy from lowest to highest is:

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