When we export goods with payment of IGST and charge sea/air freight in export bill separately, then what is rate of GST charge on the freight?

Freight in exports is no separate supply but an incidental supply to the supply of goods made by a person. Accordingly, as per Section 15(2)(c), value of supply shall include incidental expenses, including commission and packing, charged by the supplier to the recipient of a supply and any amount charged for anything done by the supplier in respect of the supply of goods or services or both at the time of, or before delivery of goods or supply of services. Accordingly, freight is to be included in the value of exports and is not to be considered as a separate supply. Accordingly, in my humble opinion, rate of tax as applicable on goods shall be applicable on freight as well.