An element X is represented as ³¹₁₅X. What is the composition of its nucleus?

Correct Answer: 15 protons and 16 neutrons

Subject: chemistry

• 31 protons and 15 neutrons
• 15 protons and 16 neutrons
• 15 protons and 31 neutrons
• 16 protons and 15 neutrons

Explanation: • <b>Key Fact</b> In notation ᴬ_Z X, Z is atomic number (protons) and A is mass number (protons + neutrons). • <b>Supporting Detail</b> Protons (Z) = 15. Mass number (A) = 31. Neutrons (N) = A - Z = 31 - 15 = 16. • <b>Related Concept</b> The element with atomic number 15 is Phosphorus. • <b>Why wrong options are wrong</b> Option A incorrectly makes mass number the proton count. Option D swaps proton and neutron counts. • <b>Exam Trick</b> Neutrons = Top Number − Bottom Number (31 - 15 = 16). • <b>Additional Info</b> This representation is standard across IUPAC chemistry for specifying isotopes.

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