SQL Server - SQL Server - Differences between Primary key and Unique key?

The below are the key differences between PK and UK .

S.No	Primary Key	Unique Key
1	Creates Clustered index	Creates Non-Clustered index
2	Null values are not allowed.	Allows only one null value.
3	We can have only one Primary key in a table.	We can have more than one unique key in a table.
4	Primary key can be made foreign key into another table.	Unique key cannot be made foreign key into another table.