Question

how we can find the positive or negative charge on an atom.

Answer 1

The simplest of the ways to check is
If the atom is attracted towards the negative charge It is an Positive atom or Anion
And same is vice versa i.e. Cation

Answer 2

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HERE IS YOUR ANSWER ⬇️⬇️⬇️⬇️
To find the ionic charge of an element you'll need to consult your Periodic Table. On the Periodic Table metals (found on the left of the table) will be positive. Non-metals (found on the right) will be negative. But you need to know the specific ionic charge elments.
may it help you