What is the output of below query?

declare @str1 varchar(50);
declare @str2 varchar(50);

set @str1 = 'Vishal';
set @str2= 'Kumar';

select nullif(@str1,@str2);

Output will be Vishal.

As NULLIF Returns a null value if the two specified expressions are equal.But it returns the first expression if the two expressions are not equal.

Here,@str1 and @str2 have the different values assigned that is Vishal and Kumar.
Here both variables have different values.Therefore it will return 1st argument value that is Vishal.