Question

What is the unit of SAR (sodium adsorption ratio)?

• A. Moles/litre
• B. me/litre
• C. (me/litre)$^{0.5}$
• D. (Moles/litre)$^{0.5}$

Hint:

SAR units:
- SAR = Na$^+$ $\sqrt{(\text{Ca}^{2+} + \text{Mg}^{2+})/2}$.
- Units: (me/L)$^{0.5}$.
- Used to assess sodium hazard in irrigation water.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
This question tests knowledge of the units of the sodium adsorption ratio (SAR).

Step 2: Detailed Explanation:
SAR is calculated as:
\[ \text{SAR} = \frac{\text{Na}^+}{\sqrt{\frac{\text{Ca}^{2+} + \text{Mg}^{2+}}{2}}} \] where concentrations are expressed in me/L.
The numerator has units of me/L.
The denominator has units of (me/L)$^{0.5}$.
Thus, the overall unit of SAR is (me/L)$^{0.5}$.
Option A (Moles/litre) and B (me/litre) are incorrect.
Option D (Moles/litre)$^{0.5}$ is incorrect because concentrations are in me/L.
Thus, the correct unit is (me/litre)$^{0.5}$.

Step 3: Final Answer:
Thus, the unit of SAR is (me/litre)$^{0.5}$, which corresponds to option (C).
[0.5cm]