Question

An element X combines with oxygen to form an oxide X$_2$O. To which group of the periodic table does the element X belong?
(A) Group 1
(B) Group 3
(C) Group 5
(D) Group 7

Answer 1

Hint: The group can be checked by knowing the valency of X. We can write the chemical equation to know the valency.

Complete step by step answer:
X belongs to the group 1 of the periodic table.
- The chemical equation can be written as:
2X$^{+1}$ + O $^{2-}$ $\rightarrow$ X$_2$O
- From the chemical equation we know that X has a valency of +1.
- From the above given options, +1 valency has been shown by group 1 elements.

Group 1 elements are Li, Na, K, Rb, and Cs known to be alkali metals. These are soft in nature and have low melting points.
Thus, element X belongs to the group 1.
So, the correct option is A.

Note: Don’t get confused between the different groups. Each group represents different properties in the periodic table so it is easy to predict the element by the valency. Since two atoms of metal atom combined with one oxygen atom therefore valency of metal atom should be 1.