Question
What is lightning?

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Column I
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Column II
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$a.$
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Inorganic impurities
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$i.$
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Phosphorus and nitrogen
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$b.$
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Organic impurities
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$ii.$
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Nitrates and phosphates
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$c.$
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Nutrients
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$iii.$
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Cholera and typhoid
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$d.$
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Bacteria
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$iv.$
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Pesticides and herbicides
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