What is the difference between partial and abstract classes ?

An abstract class has no implementation of its members. The implementation has to be provided by derived classes.
A partial class is the same class split into two different files.

so a partial class is just used to sub divide a large class into smaller ones so that it is easy to use and work with ?

but can an abstract class be instantiated ?

but can an abstract class be instantiated ?

No. That's the point, you're forced to derive from an abstract class.