Hi Karthick,All those terms are defined and differentiated as follows:
Null– Its a Trait.
null– Its an instance of Null- Similar to Java null.
Nil– Represents an emptey List of anything of zero length. It's not that it refers to nothing but it refers to List which has no contents.
Nothing - is a Trait. It's a subtype of everything. But not superclass of anything. There are no instances of Nothing.
None– Used to represent a sensible return value. Just to avoid null pointer exception. Option has exactly 2 subclasses- Some and None. None signifies no result from the method.
Unit– Type of method that doesn’t return a value of anys sort.
