Chemistry
Cement is made hard with

Dissociation of water
Polymerisation
Dehydration
Hydration and dissociation of water

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Chemistry
Sodium vapour lamps glow with yellow colour. This is due to

Its ability to absorb all other colours except yellow
The emission of excess energy absorbed by sodium atoms, in the yellow region of the spectrum
sublimation of sodium to emit yellow colour
The low ionisation energy of sodium

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