Question

How many lone pairs of electrons are represented in the Lewis structure of a phosphate ion (PO43-)? 10 12 21 24

Answer 1

To illustrate the Lewis structure,
P has 5 valence electrons
O has 6 valence electrons (each for 4 oxygen)
And finally, for every negative charge, there is an additional valence electron

We should add these all up = 5 + 24 + 3 = 32 valence electrons

With this, we can be guided to illustrate the lewis structure as P as central atom and the 3 oxygen each with a single bond with P and 1 oxygen with a double bond with P. We place the valence electrons until octet rule is satisfied,
we will be left with 12 lone pairs for phosphate ion.