$A$ shiny brown coloured element $X$ on heating in air becomes black in colour. Name the element $X$ and the black coloured compound formed.

(N/A) $X$ is copper $(Cu)$ and the black-coloured compound formed is copper oxide $(CuO)$.
The chemical reaction that occurs when copper is heated in air is as follows:
$2Cu (s) + O_2 (g) \xrightarrow{\text{Heat}} 2CuO (s)$
In this reaction,copper reacts with oxygen to form copper$(II)$ oxide,which is black in colour.