Explanation:
The valency of the element is the measure of the combining power of the element with the other atoms when the element forms compounds or molecules.
<u>Thus, valency has to known to find the how the elements have been combined and how many electrons have been lost, gain or shared.</u>
Given that:
Element A has 3 valence electrons and element B has 2 valence electrons. To find the ionic compound, the valency of the cations and the anions are interchanged and are written in subscripts. Thus,
A B
3 2
Cross multiplying, we get the formula :
<u>Hence, 3 is the subscript for Element B.</u>