Index Properties MCQ with answer and solution

Concept

Oven drying at 105-110 °C is the standard and most accurate lab method for water content of any soil.

Formula

w = (W₁ - W₂) / W₂ × 100, where W₁ = wet soil weight, W₂ = dry soil weight

Step-by-step solution

1. List the methods: oven drying, calcium carbide, pycnometer, torsion balance. 2. Oven drying fully removes free water at a controlled 105-110 °C for about 24 hours. 3. The other methods are quick field or rapid methods and are less accurate. 4. So the most accurate method is the oven drying method.

Explanation

The oven drying method is the standard lab method for water content. The soil is dried at 105-110 °C until its weight stays constant, so the result is the most accurate. The other methods are faster but less accurate.

Why the other options are wrong

A: Torsion balance (infrared) is a quick method, less accurate. C: Calcium carbide is a rapid field method, needs a calibration, less accurate. D: Pycnometer is a quick method for cohesionless soil, but it needs G known and is less accurate than oven drying.

Shortcut

Most accurate water content for any soil = Oven drying (standard method).

Common mistake

Choosing pycnometer because it is suited to cohesionless soil. It is quick, not the most accurate.