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

The low ionisation energy of sodium
sublimation of sodium to emit yellow colour
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

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Chemistry
The main use of salt in the diet is to

increase the solubility of food particles in water
produce in small amounts the hydrochloric acid required for the digestion of food
ease the process of cooking
make the taste of food better

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