Question

Define the term valency. What is the valency for magnesium and copper

Answer 1

valency is number of electrons gain or loss to achieve noble gas configuration I.e. fully filled octet.
valency of mg= -2
valency of copper= +1 or +2

Answer 2

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The combining capacity of the atoms in a element is known as valency.

Valency of magnesium:

2

Valency of copper:

2,1