CBSE Class 10 Science 2020 · Paper 31/3/1 · Question 15

(i) White to grey: silver chloride decomposes in sunlight into grey silver and chlorine gas, $2\text{AgCl}(s)\stackrel{\text{sunlight}}{\to }2\text{Ag}(s)+{\text{Cl}}_2(g)$. (ii) Reddish brown to black: copper combines with oxygen to form black copper(II) oxide, $2\text{Cu}(s)+{\text{O}}_2(g)\stackrel{\text{heat}}{\to }2\text{CuO}(s)$. (iii) Blue to colourless: zinc, being more reactive than copper, displaces it and forms colourless zinc sulphate, $\text{Zn}(s)+{\text{CuSO}}_4(aq)\to {\text{ZnSO}}_4(aq)+\text{Cu}(s)$; a reddish-brown coating of copper forms on the zinc.