Suppose the price of 1 kg of a goods be \(Rs. 100\).
So, the price of 800 gm of the goods = \(Rs. 80\)
Discount offered on the goods = \(20\%\space of Rs. 100 = Rs. 20\)
So, the selling price of the goods = \(Rs. 80\space per \space kg\)
Therefore, the cost price and the selling price of 800 gm of the goods are same.
Hence, there is no profit or loss.
\(\therefore\)The correct answer is C