NRCS (USDA-SCS) Hydrologic Soil Groups classification:
Group A: Deep sand or gravel; very high infiltration rate ($\gt 0.75\text{ cm/h}$); low runoff potential (Statement A is false, B is true).
Group B: Moderately deep to deep, moderately fine to moderately coarse textures (loam/silt loam); moderate infiltration rate ($0.38 - 0.75\text{ cm/h}$); moderately low runoff potential (Statement D is false).
Group C: Soils with impeding layer or moderately fine/fine texture (clay loams); slow/low infiltration rate ($0.13 - 0.38\text{ cm/h}$); moderately high runoff potential (Statement C is true).
Group D: Heavy clays with high swelling, high water table, or shallow over impervious layer; very low infiltration rate ($\lt 0.13\text{ cm/h}$); high runoff potential (Statement E is false).

Standard rules for sharp-crested weir installation for accurate discharge measurement:
Statement (C) is true: The head over the weir (\(H\)) must be measured at an upstream distance of at least \(4H\) to \(5H\) (typically 4 times maximum head) to avoid the drawdown (surface curve) effect immediately preceding the crest.
Statement (A) is false: The approach velocity must be kept low ($\lt 0.15\text{ m/s}$) or explicitly accounted for in discharge calculations.
Statement (B) is false: The height of the crest above the channel bottom must be at least \(2H\) to \(3H\) (NOT closer than \(2H\)) to prevent contraction suppression.
Statement (D) is false: Free flow with adequate nappe aeration underneath is mandatory to prevent suction and measurement errors.

Head loss due to friction in pipe flow is calculated using the Darcy-Weisbach formula:

where

In meteorology and instrumentation:
Statement (II) is correct: The most widespread, reliable, and standard method for determining atmospheric relative humidity in weather stations and observatories is the psychrometer, which employs paired dry and wet bulb thermometers (e.g., Assmann psychrometer, sling psychrometer, or Stevenson screen thermometers).
Statement (I) is considered incorrect in standard examination conventions: A hygrometer (such as a hair hygrometer or mechanical hygrometer) measures changes in physical dimensions or electrical resistance/capacitance caused by moisture absorption, rather than measuring relative humidity as a fundamental primary dimension directly without empirical scaling. Furthermore, in standard meteorological practice, relative humidity is derived from dry and wet bulb temperature depression via psychrometric tables/formulas rather than standalone direct dial hygrometers.
Consequently, Statement (I) is incorrect and Statement (II) is correct.