Question

what is variable valency in chemistry

Answer 1

those which have more than one valency

Answer 2

However, in transition elements, an atom loses electrons from the shell next to the valence shell (penultimate shell). In such a situation the element exhibits more than one valency (variable valency). For example: Iron has 2 electrons in its valence shell. On donating these electrons, its valency is 2+.
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