Physics
Hertz is a unit for measuring

Clarity of waves
Wavelength
Intensity of waves
Frequency of waves

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Physics
Rainbow is due to

ionisation of water deposits
refraction and reflection of sunlight by water droplets
diffusion of sunlight through water droplets
absorption of sunlight in minute water droplets

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Physics
Thermohaline circulation is mainly due to

Cold, dense ocean water sinking and warmer water replacing it
Warmer, less dense water sinking in the ocean and cold water replacing it
Warm water being added to the ocean due to industial waste
Winds causing circulation of ocean water

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