Question

what is the reason behind variable valency

Answer 1

The electrons present in the outermost shell of an atom are called valence electrons. If the valency electrons are removed, the remainder is called Core.

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Answer 2

ʜᴏʟᴀ ᴍᴀᴛᴇ !

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⭐ᴀɴsᴡᴇʀ⭐

Certain elements have more than one valency. They exhibit variable valency. For example, copper, tin, iron and mercury exhibit variable valency. Copper combines with oxygen to form cuprous oxide (Cu2O) and cupric oxide (CuO).