Upgrade to access all content for this subject

Which of the following topological spaces is NOT a Hausdorff space?

$\mathbb{R}$ with the standard (metric) topology.

The Euclidean plane $\mathbb{R}^2$ with the standard (metric) topology.

$\mathbb{R}$ with the discrete topology.

$\mathbb{R}$ with the trivial topology $\{\emptyset, \mathbb{R}\}$

The unit interval $[0,1]$ with the topology given by the usual Euclidean metric on $\mathbb{R}$ restricted to $[0,1]$.