Unit 1

• Capillary Water Potential:
• Capillary rise of water in soil pores or glass tubes occurs against gravity due to surface tension and adhesive forces.
• Water held in the capillary meniscus above a free water table is under hydrostatic suction/tension, existing at sub-atmospheric pressure characterized by a negative pressure potential (matric potential, $\psi_p \lt 0$). (Correct answer: Option 2)

• Chlorine Hydrolysis Chemistry: When chlorine gas ($\text{Cl}_2$) dissolves in water, it hydrolyzes almost instantaneously to form hypochlorous acid ($\text{HOCl}$) and hydrochloric acid:

$$\text{Cl}_2 + \text{H}_2\text{O} \rightleftharpoons \text{HOCl} + \text{H}^+ + \text{Cl}^-$$

Hypochlorous acid then partially dissociates based on water $\text{pH}$:

$$\text{HOCl} \rightleftharpoons \text{H}^+ + \text{OCl}^-$$

• Disinfection Efficacy: Hypochlorous acid ($\text{HOCl}$) is electrically neutral and lipophilic, allowing it to rapidly penetrate negatively charged bacterial cell walls and membranes (roughly 80 to 100 times more germicidal than the negatively charged hypochlorite ion, $\text{OCl}^-$).
• Conclusion: Both Statement (I) and Statement (II) are correct.

Correct option: (1) Both Statement (I) and Statement (II) are true.

• Thornthwaite Moisture Index ($I_m$) Scale (1948):
• Perhumid ($A$): $I_m \ge 100$
• Humid ($B_4$ to $B_1$): $I_m = 20 \text{ to } 100$ ($B_2$-Humid corresponds to 40 to 80)
• Moist Subhumid ($C_2$): $I_m = 0 \text{ to } 20$
• Dry Subhumid ($C_1$): $I_m = -33.3 \text{ to } 0$ (or $-20 \text{ to } 0$)
• Semiarid ($D$): $I_m = -66.7 \text{ to } -33.3$
• Arid ($E$): $I_m = -100 \text{ to } -66.7$
• Systematic Matching:
• $B_2$-Humid corresponds to 40 to 80
• E-Arid corresponds to -100 to -66.7
• D-Semiarid corresponds to -66.7 to -33.3
• $C_2$-Moist subhumid corresponds to 0 to 20.

Correct option: (3) (A) - (IV), (B) - (II), (C) - (IN), (B)- (1)