Hey please can anyone tell me thatin formula making how can we get the valency of for example So4 in2Na + H2So4➡Na2So4so how can we know that we have to put 2Na if we dont know the formula and are suddenly asked to write the formula of Sodium sulphate???please help me with this

Hey please can anyone tell me thatin formula making how can we get the

1.	Hey please can anyone tell me thatin formula making how can we get the valency of for example So4 in2Na + H2So4➡Na2So4so how can we know that we have to put 2Na if we dont know the formula and are suddenly asked to write the formula of Sodium sulphate???please help me with this
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