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2020 O Level Chem P1 Q6 — Atomic Structure / Nucleon and Proton Number Solution

Atomic Structure / Nucleon and Proton Number 2020 O Level Pure Chemistry · Paper 1 · Q6

Question

A new element was first synthesised in 2006. It has been given the name oganesson and is represented by ²⁹⁴₁₁₈Og. Which statement about an atom of oganesson is correct?

AIt contains 118 electrons and 176 nucleons.
BIt contains 118 electrons and 176 protons.
CIt contains 118 protons and 176 neutrons.
DIt contains 118 protons and 176 nucleons.

Correct answer: C

Video Solution

Explanation

Answer: C (118 protons and 176 neutrons). In the nuclide notation \(^{294}_{118}\text{Og}\), the lower number is the proton number \(Z = 118\) and the upper number is the nucleon (mass) number \(A = 294\).

So the atom has 118 protons. The number of neutrons is the nucleon number minus the proton number: \(294 - 118 = 176\). Because oganesson here is a neutral atom, the number of electrons equals the number of protons, which is 118.

Checking the options: A and B wrongly state 176 nucleons or 176 protons, but the nucleon number is 294 and the proton number is 118. D wrongly calls 176 the nucleon number, when 176 is actually the neutron count. Only C correctly pairs 118 protons with 176 neutrons.

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