Detailed Evaluation of Septic Tank Functions:

• Storage of sludge and scum is True: Heavy settleable solids settle to the bottom as sludge, and grease/oil floats to form a scum mat at the surface, where both accumulate until periodic desludging.
• Removal of solids from the sewage is True: Quiescent settling in the chamber removes 60–70% of suspended solids from incoming sewage.
• Decomposition under aerobic conditions is False: A septic tank is an enclosed, unventilated subterranean chamber where dissolved oxygen is rapidly depleted, so aerobic treatment cannot occur.
• Decomposition under anaerobic conditions is True: Facultative and anaerobic bacteria digest settled organic solids, converting them into stable humic sludge, water, and gases ($\text{CH}_4$, $\text{CO}_2$, $\text{H}_2\text{S}$).

Calculation of Gypsum Requirement by Schoonover Method:

• Principle: Schoonover's method determines gypsum requirement by equilibrating alkali soil with saturated gypsum solution. Exchangeable sodium is replaced by calcium ions, and the reduction in dissolved calcium concentration measures the exchange capacity requiring replacement.
• Given Data:
  Volume of gypsum solution ($V$) = $100\text{ mL} = 0.1\text{ L}$
  Initial concentration ($C_{\text{initial}}$) = $36\text{ meq/L}$
  Final concentration in filtrate ($C_{\text{final}}$) = $32\text{ meq/L}$
  Soil sample mass ($W$) = $5\text{ g}$
• Amount of Calcium Adsorbed by Soil Sample:
  $$\Delta C = 36 - 32 = 4\text{ meq/L}$$
  $$\text{Ca adsorbed by } 5\text{ g soil} = 4\text{ meq/L} \times 0.1\text{ L} = 0.4\text{ meq}$$
• Gypsum Requirement per $100\text{ g}$ of Soil:
  $$\text{GR} = \frac{0.4\text{ meq}}{5\text{ g}} \times 100\text{ g} = 0.4 \times 20 = 8\text{ meq/100g of soil}$$

Therefore, the gypsum requirement is 8 meq/100g of soil (Option 2).