Past exam of the topology course of the University of Oxford / 2023 / 2 / b / ii

False. Give $X=\mathbb{R}$ its usual topology, identify all points of $(0,1)$ with one another, and leave every other point in a singleton equivalence class. Take the closed set $K=\{1/2\}$.

Its image $p(K)$ is a singleton in the quotient space, but its full preimage, also called the saturation of a subset, isThis is not closed in $\mathbb{R}$, since $0$ belongs to its closure. In the quotient topology, a subset is closed exactly when its preimage is closed, by applying the defining open-set rule to complements. Thus $p(K)$ is not closed, and this quotient map is not a closed map.