Question

Element with atomic number 15 and mass number 31 is present in:
a.) Group 5 and period 4
b.) Group 15 and period 3
c.) Group 5 and period 3
d.) Group 15 and period 4

Answer 1

Element in the given question is Phosphorous (P) and we just have to find the electronic configuration of this element and from it we can figure out the period and the group number of the element.

Complete step by step answer:
Element of atomic number 15 is Phosphorous (P) which is a non-metal and a member of p-block. The electronic configuration of Phosphorus is given as $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{3}}$.
As we can see the valence electrons belong to 3p subshell so it belongs to p-block and 3rd period and the highest shell occupied is 3p. As the number of valence shell electrons are 5 the element will belong to the 15th group which is the Nitrogen family. Hence, we infer that the given element belongs to the fifteenth group and third period of the modern periodic table.
Hence, the correct answer is that the element with atomic number 15 and mass number 31 is present in group 15 and period 3 . So, the correct answer is “Option B”.

Note: The s-block, p-block and the d-block elements of the periodic table are arranged into 18 numbered columns, or groups. The elements in each group have the same number of valence electrons and hence show similar chemical properties. Due to this fact the elements in the same group often display similar properties and reactivity.A period in the periodic table is a row of chemical elements where all elements in a row have the same number of electron shells. Each next element in a period has one more proton and is less metallic than its predecessor as we move left to right.