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.
The theoretical amount of product produced.
quantity demanded
This quantity is referred to as the PRODUCT.
Petrol
when the price of product increased the porchasing powre of consumer is foll so he will decreases his quantity demand for that product.
quantity suppilied
quantity suppilied
its something you use instead of that one thing.