please why Na2Co3 is called sodium carbonate (iv).i do not understand why the (iv) is mention and also H2So4,how come about the (vi) in the name (tetraoxosulphte (vi) acid

Answer 1

the iv and the vi refer to the oxidation state of Sulfur, and carbon in the compounds. For these two, it is most unusual to put the roman numerals in the name.

Answer 2

To follow up on Bob Pursley's answer, the iv and vi are unnecessary. Technically, I think it is wrong; however, everyone will know what it means.