Unique key and Primary key

Unique key : 

1) Unique key can have nulls.

2)We can create multiple unique keys on a table.

3)Unique key Creates a non-Clustered Index by default.

Primary Key :    

1)Primary key cannot have nulls.

2)We can have only one Primary key on a table.

3)Primary key Creates a Clustered Index by default.

Both Unique keys and Primary keys can be referenced by foreign key.