If $ S $ is a set having 10 elements in it and $A$ is a relation in $S$ defined as $A=\{(x,y)$, where $ x,y \in\:S\;$ and $\;x\neq\;y.\}$, then no. of elements in $A$ is

Question

$\begin{array}{1 1} 45 \\ 50 \\ 90 \\ 100 \end{array}$