Query regarding item details and Purchase A/c

Query regarding item details and Purchase A/c

A] 
Which account should be selected while creating an item?
If the purchase is related to the following transactions, please guide on which account should be selected.
1) Intra-State Purchases (CGST+SGST)
2) Inter-State Purchases (IGST)

As Sales Information has Sales A/c,
Why does Purchase Information does not have Purchase A/c?
Why can't I create Sub-Categories under Purchase and Sales A/c?


B]
In Tally, we are able to create Sub-Accounts under Purchase A/c.
But the Same is not possible in Zoho Books.
I want to keep track of Inter-State and Intra-State Purchases.
Please Guide.