1) White washing is done with the compound called slaked lime (calcium hydroxide).It reacts with carbon di oxide in air and forms calcium carbonate which gives a shiny finish on walls.
Ca(OH)2 + CO2 --> CaCO3 + H2O
2) The reaction of decomposition of light is used in this case.
When light is allowed to pass through silver chloride it decomposes to form chlorine and silver.The chlorine gas escapes and thus now the compound holds up grey color due to the presence of silver
2AgCl ---> 2Ag + Cl2
Silver silver chlorine