NCERT Question 17

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

Answer:

The shiny brown-coloured element ‘X’ is copper (Cu).

When copper is heated in air, it reacts with oxygen to form a black coloured compound called copper(II) oxide (CuO).

Reaction:

2Cu (brown) + O₂ → heat^ 2CuO