Question

what is meant by the term variable valency?​

Answer 1

In transition elements, an atom loses electrons from the shell next to the valence shell . In such a situation the element exhibits more than one valency.

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Answer 2

Valency is the capacity of an atom to lose, gain or share atoms during a chemical reaction is called its valency. Sometimes atom of an element can lose more electron than they are present which means they lose electron from its penultimate shell. Such an element is said to exhibit variable valency.