What is the output of below sql query?

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

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

select nullif(@str1,@str2);

Output will be Null,

As NULLIF Returns a null value if the two specified expressions are equal.

Here,@str1 and @str2 have the same values assigned that is Vishal.NullIf does not check whether expressions are case-sensitive.It checks only expression values.
Here both variables have same values.Therefore it will return Null.