Physics
Rainbow is due to

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

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Physics
Lightning is produced when

Clouds strike against impurities in air and the friction burns up these impurities
Strong opposite charges in different clouds break down the resistance offered by the intervening air
Similar charges of electricity rush towards each other and then get repelled
Water vapour produces electricity in the clouds

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