Correct option is B
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Correct answer: (b) 20-50 nm
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Nano Urea particles in India have an average size range of
20-50 nm, which makes them highly efficient in nutrient uptake by plants.
Other options:
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(a) 1-20 nm: Too small for Nano Urea particles; this range is typically too fine for efficient usage in agriculture.
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(c) 50-100 nm: Slightly larger than the usual size range for Nano Urea particles.
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(d) 100-200 nm: Too large for the optimal nano size, which is generally around 20-50 nm.