Answer : B
$S_1 : $ $\forall x \exists y \forall z(x + y = z)$, Where domain is Real Numbers.
It is Saying that For each real number, say $x = 5$, there is some real number $y$ such that $x+ y = z$, for all real numbers $z$.
This is False as it says that $5 + y = ALL \,\,Real\,\,Numbers$, Where $y$ is some fix real number. This is obviously wrong.
$S_2 : $ $\exists x \forall y \exists z(x + y = z)$, Where domain is Real Numbers.
It says that There is some Real number, say $x$, such that for each real numbers $y$, $x + y = z$ for some real number $z$(may be different values of $z$ for different values of $y$).
It is True. As Say you take $x = 5$, then You can add Any Real number $y$ to it and It will result in some real number(not necessarily same for each $y$)
Note : Actually, $S_2$ is a subset condition of the following formula :
$\forall x \forall y \exists z(x + y = z)$, Where domain is Real Numbers. Which is True as For Every Pair of real numbers, say $(5,7)$, we do have Some Real number $z$ such that $5+7 = z$, here, for pair $(5,7)$, $z$ is 12. For different pairs $(x,y)$, $z$ may be different but it will surely exist.