Question

The atomic number of elements A, B, C and D are ${\text{Z}} - 1,{\text{ Z, Z}} + 1{\text{ and Z}} + 2$ , respectively. If ‘B’ is a Noble gas, choose the correct answer from the following statements.
1.‘A’ has higher electron affinity
2.‘C’ exists in $+ 2$ oxidation state
3.‘D’ is an alkaline earth metal
A.$(1){\text{ and (2)}}$
B.$(2){\text{ and (3)}}$
C.$(1){\text{ and (3)}}$
D.$(1),{\text{ (2) and (3)}}$

Answer 1

Every element wants to get noble gas electronic configuration. To attain noble gas electronic configuration an element loses or gains an electron depending upon whether it has extra electron or less electron than corresponding noble gas. Electron affinity is the tendency of an element to gain electrons.

Complete step by step solution:
It is given to us that element B is a noble gas that has a completely filled valence shell electronic configuration. They are the most stable elements in the periodic table and they neither accept electrons nor lose electrons. The atomic number of ‘B’ is ${\text{Z}}$.
When one electron is removed from the noble gas the atomic number will become ${\text{Z}} - 1$ . The element with ${\text{Z}} - 1$ atomic number is ‘A’. To attain noble gas electronic configuration it just requires one more electron and hence will have a strong tendency to gain electrons. So the element must have high electron affinity. So the statement 1 is correct.
The element C has an atomic number as ${\text{Z}} + 1$ . After losing one electron its atomic number will be the same as noble gas and hence it will readily lose one electron and not more than 1. The element C will exist in $+ 1$ oxidation state and not $+ 2$.
In the same way the element D will lose 2 electrons, because after losing 2 electrons it will attain noble gas electronic configuration. We know group number 2 elements lose 2 electrons and are known as alkaline earth metals, so the statement 3 is correct.

The correct option is C.

Note: We can understand the above analogy with an example. Let the noble gas ‘B’ be Neon. Then sodium will be the element ‘C’ and magnesium will be the element ‘D’. Fluorine will be the atom ‘A’. We know magnesium is an alkaline earth metal.