Indiscrete topology ($\{\varnothing ,X\}$)

The indiscrete topology on a set $X$ has only the empty set and the whole set as open sets. When $X$ has more than one point it is not a Hausdorff space. For example the quotient topology on $\mathbb{R}/\mathbb{Q}$ is indiscrete: a nonempty open saturated subset contains an interval and all its rational translates, which cover $\mathbb{R}$.