Why do I have the feeling that your question is not well-phrased?
You probably don't want your instant mix to be sour in taste, and you're looking for a substitute for citric acid...
A close substitute of a product is one which can easily replace it - eg margarine is a close substitute of butter. Two products are substitutes if they have a positive cross-elasticity - as the price of one increases, the quantity of the other increases
It depends. If sodium bicarbonate is added to something in a chemical reaction, then it is a reactant in this case. If a chemical reaction forms sodium bicarbonate, then it is a product.
On possible substitute is coffee syrup, though the sugar will need to be reduced in the recipe. Coffee syrup however is mainly a regional product with more than 95% of it being produced and consumed in Rhode Island, USA. Otherwise there is little which can replace instant coffee without changing the taste.
The quantity supplied is the quantity of a product that is produced and sold at a specific price.
Petrol
The theoretical amount of product produced.
its something you use instead of that one thing.
This quantity is referred to as the PRODUCT.
quantity demanded
Petrol
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