scarcity

In Economics, scarcity arises because resources are limited, however, people wants are unlimited. Therefore, resources cannot be allocated efficiently. Resources can be refered as 3 basic types, i.e. land, labor and also capital.
Land refers to the natural resources, capital includes not just the investment of the entrepreneur, but also equipment, machine, etc.
In addition, because of scarcity, there is opportunity cost.

And for surplus, it arises mainly becasue the market supply is larger than market demand.
This may be caused by a variety of reasons.

Hope this can help you to solve your problem :-)