iGCSE Chemistry (0620) Core:8.5 Noble gases: Exam Style Questions Paper 1- New Syllabus
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Detailed solution:
Noble gases are characterised by having completely filled outer electron shells, which makes them exceptionally stable and chemically unreactive. For most noble gases (neon, argon, etc.), this means eight electrons in the outermost shell, following the octet rule. Helium is the exception with a full outer shell of just two electrons. In the diagrams shown, diagram 2 likely has an incomplete outer shell (perhaps 7 electrons or fewer), which would belong to a reactive element like a halogen or other non-metal, not a noble gas. Diagrams 1 and 3 both show completely filled outer shells—whether that means 2 for helium or 8 for neon/argon. Therefore, the set that correctly identifies noble gas configurations is 1 and 3.
▶️ Answer/Explanation
Detailed solution:
The description fits noble gases from Group VIII. Argon and krypton both have a full outer shell of eight electrons and exist as single atoms. Helium is a noble gas that exists as single atoms and is unreactive, but it only has two electrons in its outer shell, not eight, because its first shell is complete with just two. Oxygen is not a noble gas at all—it is diatomic, reactive, and has six outer electrons. So only argon and krypton perfectly match all three parts of the description: monatomic, unreactive, and with eight outer electrons.
▶️ Answer/Explanation
Detailed solution:
Noble gases are monatomic gases, so statement 3 is correct. However, helium only has 2 outer electrons, not 8—so statement 1 is incorrect. Their full outer shells make them very unreactive; they do not easily react with sodium to form ionic compounds, so statement 2 is incorrect. Only statement 3 is correct.