What is the difference between stocks …

Stock :-
Resources that satisfies human needs
These have not been utilized yet.
The reason is due to lack of technology
Example :-  Water [ it satisfies our needs , but we cant make water ourselves by combining hydrogen and water { lack of technology } ]

Reserves :-
These resources can be utilized by using appropriate technology.
Even after having technology to utilize it , it has been kept aside for future requirements
Example :-
Water in dams 

Stock:

The resources that satisfies the human needs
These are not being accessed due to lack of technology
Eg: Minerals found in the see satisfy our needs but we cant obtains them because of lack of Technology
Reserves:

Reserves are subset of of the stocks
These are being accessed with the existing technology
But their uses are not started yet
Eg: Forests, reservoirs, Dams etc.,