Question

The most commonly used unit for expressing the total quantity of dissolved salts present in a given water sample is

• A. decisiemens per meter
• B. siemens
• C. gm per liter
• D. decisiemens

Hint:

Salinity units: $1\text{ dS/m} = 1\text{ mmhos/cm} = 1000\text{ }\mu\text{S/cm} = 1000\text{ }\mu\text{mhos/cm}$.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Water salinity is standardly quantified by measuring the electrical conductivity ($EC$) of the solution, which correlates directly with total dissolved solids ($TDS$).
Key Formula or Approach:
\[ \text{TDS (mg/L or ppm)} \approx 640 \times EC \text{ (in dS/m)} \quad (\text{for } EC < 5\text{ dS/m}) \]

Step 2: Detailed Explanation:
Under standard SI and international soil/water chemistry conventions (USSL FAO-29):
Electrical conductivity ($EC$) is the universal index used to express salinity.
The standard unit is decisiemens per meter ($\text{dS/m}$ or $\text{dS m}^{-1}$), which is numerically identical to the classical unit millimhos per centimeter ($\text{mmhos/cm}$).

Step 3: Final Answer:
Therefore, the most commonly used unit is decisiemens per meter, matching option (A).