WAEC Chemistry 2025 Paper

Concept:The electron configuration reveals the atomic number, period, group, and number of unpaired electrons of an element.Explanation:Add the superscripts: $2+2+6+2+4=16$, so the atomic number of Y is $16$.The highest principal quantum number is $n=3$, which places Y in period 3, not period 4.The valence shell is $3s^2 3p^4$, containing $2+4=6$ valence electrons, so Y belongs to group VI.For the $3p^4$ subshell, the three p orbitals hold four electrons as $\uparrow\downarrow$, $\uparrow$, and $\uparrow$, meaning there are only two unpaired electrons, not three.The mass number cannot be determined from the electron configuration alone because isotopes of the same element have different mass numbers.Answer:Y belongs to group VI.Therefore, the correct option is D.