user21183: 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.

user88292: Blockchain Data API
https://www.blockchain.com/api/blockchain_api:

Single Block

https://blockchain.info/rawblock/$block_hash
You can also request the block to return in binary form (Hex encoded) using ?format=hex



user12983: 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

21183: <p>Is there any Web API available for us to query Blockchain data in hex format? </p>

<p>The format should follow the standard (<a href="https://en.bitcoin.it/wiki/Block#Block_structure" rel="noreferrer">https://en.bitcoin.it/wiki/Block#Block_structure</a>) structure rather than JSON.</p>
 88292: <p>Blockchain Data API
<a href="https://www.blockchain.com/api/blockchain_api" rel="nofollow noreferrer">https://www.blockchain.com/api/blockchain_api</a>:</p>
<blockquote>
<p>Single Block</p>
<ul>
<li><code>https://blockchain.info/rawblock/$block_hash</code></li>
<li>You can also request the block to return in binary form (Hex encoded) using ?format=hex</li>
</ul>
</blockquote>
 12983: <p>What kind of API do you want? Do you mean API with your local Bitcoin Core or do you need web-API?</p>

<p>Have a look to <a href="http://webbtc.com/block/000000000000000001f942eb4bfa0aeccb6a14c268f4c72d5fff17270da771b9" rel="nofollow noreferrer">http://webbtc.com/block/000000000000000001f942eb4bfa0aeccb6a14c268f4c72d5fff17270da771b9</a> (this is an example)</p>

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

<p>UPDATE (december'17):
block in raw hex example : <a href="https://blockchain.info/block/000000000000000000a7b4999c723ed9f308425708577c76827ade51062e135a?format=hex" rel="nofollow noreferrer">https://blockchain.info/block/000000000000000000a7b4999c723ed9f308425708577c76827ade51062e135a?format=hex</a></p>
