How do you get a defficate when doing the lewis dot structure in chemistry?

Question

I mean Deffacete, like H2 CO3, where you have a deffacete of 2 electrons.
Doing needs analasys
2H= 2 electrons
C = 4 e
0 = 3(6)
Total = 24 electrons
Shown = 10 electrons
Left = 14 electrons
Need = 16 electrons
so you have a deffacete of 2 electrons, but why?

Answer 1

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Answer 2

Be sure to wear diapers.