JAMB Chemistry 2020 Paper

Concept:A noble gas has a full outermost electron shell, which makes it highly stable and unreactive.Explanation:The atomic number tells us the number of electrons in a neutral atom.For $P = 4$: electron configuration is $2, 2$; the outer shell is not full.For $Q = 10$: electron configuration is $2, 8$; the outer shell has $8$ electrons, which is a full octet.For $R = 12$: electron configuration is $2, 8, 2$; the outer shell has only $2$ electrons.For $S = 14$: electron configuration is $2, 8, 4$; the outer shell needs $4$ more electrons to become stable.Only element $Q$ has a complete outermost shell of $8$ electrons.Therefore, $Q$ is the noble gas among the four elements.Answer:B. Q