The chemical used to remove organic matter from the soil during mechanical analysis is

Correct option is D

The correct answer is (D) H2O2 

Explanation:
• Mechanical analysis requires the soil to be completely dispersed into its individual primary particles (sand, silt, and clay).
• Organic matter acts as a binding agent that glues soil particles into aggregates. To get an accurate measurement of individual particle sizes, this "glue" must be removed.
• Hydrogen Peroxide ($H_2O_2$) is a strong oxidizing agent used to digest and remove organic matter. The soil is treated with $H_2O_2$ and heated until the effervescence (bubbling) stops, indicating the organic matter has been oxidized into $CO_2$ and water.

Information Booster:
• Other pretreatments in mechanical analysis include using dilute $HCl$ to remove carbonates and using a dispersing agent like Sodium Hexametaphosphate (Calgon) to neutralize charges and prevent flocculation.
• Removing organic matter is especially critical for soils high in humus, as it can significantly interfere with the settling rates.

Additional Knowledge:
• $CaCl_2$ (Option A): Often used to flocculate soil or as an extractant for measuring soil pH in a salt solution.
• $HCl$ (Option B): Used to remove calcium carbonates (lime) from the soil sample.
• $NaOH$ (Option C): A strong base, sometimes used in organic matter extraction (humic acid) but not the standard for total organic matter removal in texture analysis.