Can I sell my commodities (gold) in commodity markets ?

Yes !!! You can if you want , As the in online commodity Exchange different commodity future contract are traded whose main purpose is to avoid risk future price uncertainty through hedging , arbitraging and speculation, To understood the commodity future market mechanism go through the below image.

The above fig. shows the buying and selling activity of gold future

where buyer and seller both pay a margin amount that is 5–7 % instead of full amount of to Exchange (MCX/ NCDEX ) to buy and sell gold or accept/deliver the 1 lot of gold .

Know suppose gold price is 29000/ 10gm here seller makes a contract with buyer that he provide a delivery of 1Kg gold (1 Lot ) to buyer on or before fixed future date that would be the expiry of contract

here may be a possibility that if seller of contract can provide the delivery of 1kg gold if he have same quality gold according to Exchange contract specification , other wise he can also square his position before the expiry of contract or in intraday if he could not make delivery of gold.

here may be the seller have purchase the gold below 28500/- 10gm and he has make contract with another person to sell the gold at 29000/- where he can make profit