Raw Block data in Hexadecimals Is there any Web API available for us to query Blockchain data in hex format? 

The format should follow the standard (https://en.bitcoin.it/wiki/Block#Block_structure) structure rather than JSON.
What kind of API do you want? Do you mean API with your local Bitcoin Core or do you need web-API?

Have a look to http://webbtc.com/block/000000000000000001f942eb4bfa0aeccb6a14c268f4c72d5fff17270da771b9 (this is an example)

It is possible to download block as [json] / [hex] / [binary] there if you know the hash of the block

UPDATE (december'17):
block in raw hex example : https://blockchain.info/block/000000000000000000a7b4999c723ed9f308425708577c76827ade51062e135a?format=hex