WAEC Chemistry 2015 Paper

Concept:The position of an element in the periodic table is found from its electron arrangement, which gives both the period and the group.Explanation:A neutral atom with 15 electrons has atomic number 15.Its electronic configuration is $1s^2\,2s^2\,2p^6\,3s^2\,3p^3$, which can be written as 2, 8, 5.The period equals the number of occupied shells, which is 3.The group equals the number of valence electrons, which is 5.So the element belongs to Group 5 and Period 3.(Note: The element is phosphorus, not arsenic.)Answer:The correct option is C: Group 5 and Period 3.