Among the following, a symmetric relation is

$x$  is a multiple of  $y$  but $y$ is not multiple of $x$

$\therefore$ it is not symmetric

$x$  is a factor of  $y$  but $y$ is not factor of $x$

$\therefore$ it is not symmetric

$x$  is a subset of  $y$  but $y$ is not subset of $x$

$\therefore$ it is not symmetric

$x$  is equal to $y$  then $y$ is equal to $x$

$\therefore$ it is  symmetric