Things get tricky here

$n$ and $a$ are different real integers, where $n≥0$ and $a≥0$ . Which of the following equations have the most real pair of integral solutions $(a,n)$ for any positive integer $a$ ?

1. $\sqrt n - \sqrt{a-n} = a$ .

4. $\sqrt n + \sqrt{n-a} = a$

Type your answer (1,2,3,or 4) and try not to use luck to finish this question lol.