Thanks it worked

I re created table and renoved not null after identity property and inserted values it worked

CREATE TABLE IdentityProducts(

productid int IDENTITY(1,1),

productname nvarchar(40) NOT NULL,

categoryid int NOT NULL,

unitprice money NOT NULL)

insert into IdentityProducts(productname,categoryid,unitprice)

values

('shad',1,100)

this worked for me