a compound X when used for whitewashing of walls and forms a Shiny white colour due to formation of Y identify X and Y​

? you expect us to answer this? ? this is your schoolwork, i don't think we can with this, i think it would considering being

we can conclude that the melting point of table salt is above room temperature (it's actually 801 deg c). the melting point of mercury must be below room temperature (- 39 deg c).

the atomic number will stay the same no matter how many electrons it has, so it doesn’t decrease nor increase. it’ll only change with a different number of protons