Water Quality Parameters MCQ with answer and solution

Concept

IS 11624-1986 rates irrigation water as Low, Medium, High or Very high using RSC (in meq/L).

Formula

RSC = (CO3²- + HCO3^-) - (Ca²+ + Mg²+), all in meq/L

Step-by-step solution

1. Recall the IS 11624 RSC limits: Low < 1.5, Medium 1.5 to 3.0, High 3.0 to 6.0, Very high > 6.0 meq/L. 2. The given RSC is 1.5 to 3.0. 3. This range falls in the Medium rating.

Explanation

Residual sodium carbonate shows extra carbonate and bicarbonate over calcium and magnesium. High RSC makes soil sodic and harms crops. IS 11624 gives RSC from 1.5 to 3.0 meq/L a Medium rating.

Why the other options are wrong

A: High is for RSC 3.0 to 6.0. B: Very high is for RSC above 6.0. D: Low is for RSC below 1.5.

Shortcut

RSC limits: 1.5, 3, 6, giving Low, Medium, High, Very high.

Common mistake

Confusing the RSC limits with the EC limits (1.5, 3, 5 dS/m) or the SAR limits (10, 18, 26).