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GATE 2021 ES – Question 44

Water Resources and Environmental Hydraulics · Global Water Resources · 2 marks · Multiple choice

Water containsNa⁺92,K⁺19.5,Ca²⁺40,Mg²⁺24 mg/L. Atomic masses Na23,K39,Ca40,Mg24. Find SAR for irrigation assessment.

  1. 2.83
  2. 1.94
  3. 2.00
  4. 4.00

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Correct answer: (A) 2.83

Explanation

Convert to meq/L:Na=92/23=4,Ca=40/20=2,Mg=24/12=2. Then $SAR=4/\sqrt{(2+2)/2}=2.82843$. Thus **2.83,A**. Potassium is not included in the standard SAR definition.