Soil pH is measured by making soil : water suspension in the ratio of

Correct option is C

The correct answer is (C) 1:2.5

Explanation:
• Soil pH is a measure of the acidity or alkalinity of the soil solution, which significantly affects nutrient availability and microbial activity.
• The standard laboratory procedure for measuring soil pH involves creating a soil-water suspension. In India and many international standards, the most common ratio used is 1 part soil to 2.5 parts distilled water (1:2.5).
• Increasing the water content (dilution) usually increases the measured pH slightly because it dilutes the concentration of hydrogen ions ($H^+$) in the solution.
• The mixture is stirred and allowed to stand before the reading is taken using a glass electrode pH meter.

Information Booster:
• Some labs also use a 1:1 ratio or a 1:5 ratio depending on the specific soil type (e.g., highly organic or saline soils).
• pH can also be measured using $0.01 M$ $CaCl_2$ solution instead of water to mask the effects of varying salt concentrations in the soil.
• A pH of 7.0 is neutral; below 7.0 is acidic, and above 7.0 is alkaline.

Additional Knowledge:
• 1:10 (Option A): Rarely used as it over-dilutes the soil solution, leading to inaccurate readings for agricultural purposes.
• 1:1 (Option D): Common in some US-based soil testing protocols but provides a lower pH reading than the 1:2.5 ratio.