Question: A shiny brown-coloured element ‘X’ on heating in the air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.
Answer: ‘X’ is copper (Cu) and the black-coloured compound formed is a copper oxide (CuO). The equation of the reaction involved in heating copper is given below.
2Cu +O₂ + Heat ⟶ 2CuO (Black in Colour)
