Question

An element ‘A’ is tetravalent and another element ‘B’ is divalent. The formula of the compound formed from these element will be;
A. ${{\text{A}}_{\text{2}}}{\text{B}}$
B. ${\text{AB}}$
C. ${\text{A}}{{\text{B}}_2}$
D. ${{\text{A}}_2}{{\text{B}}_3}$

Answer 1

Element ‘A and B’ have a valence of 4 and 2 respectively. The valency of an element determines its combining power, especially its ability to displace or add, number of hydrogen atoms. To form a chemical formula we need an equal number of valence for both the elements.

Complete step by step answer:
According to the question a tetravalent element ‘A’ is combined with a divalent element ‘B’ ,Which means one atom of ‘A and B’ has 4 and 2 valences respectively.

For a compound to be formed we need the balance in their valence. To form a compound with an element of 4 valances, we need another element of 4 valances. But we are given a divalent ‘B’ element as a counterpart of tetravalent element ‘A’.

Therefore, we need to use 2 atoms of ‘B’, for every one atom of ‘A’. Since the combined valence of ${{\text{B}}_2}$ will be 4.${\text{A}}{{\text{B}}_2}$ will be the molecular formula according to the required conditions.

Hence, the correct answer is option (C) i.e., ${\text{A}}{{\text{B}}_2}$

Note: In the chemical formula ${\text{A}}{{\text{B}}_2}$, the ${{\text{B}}_2}$ signifies two atoms of element ‘B’ and not the di-valence of the element. If we were to use 4 atoms of element ‘A’, then we will have to use 8 atoms of element ‘B’ to balance the overall 8 valances ${{\text{A}}_4}$. But this condition will not change the end molecular formula i.e., the molecular formula, in this case, would be ${{\text{A}}_4}{{\text{B}}_8}$ this can also be written as ${\text{A}}{{\text{B}}_2}$ (since 4 and 8 are divisible).