• H. Roberts (1973) categorized seeds based on their storage physiology into orthodox and recalcitrant:
• Orthodox seeds: Can survive extreme desiccation down to low moisture contents ($\lt 5\%$) and can be safely stored at sub-zero temperatures ($-18^\circ\text{C}$) for decades in gene banks. Examples include cereals and field crops like Sorghum (A) and Cotton (D).
• Recalcitrant seeds: Cannot survive drying below critical moisture thresholds ($20 - 30\%$) and are chilling-sensitive; they lose viability rapidly if dried or frozen. Examples include tropical fruit trees like Mango (B), Sapota (C), Jackfruit, and Rubber.
• Therefore, the orthodox seeds are (A) and (D) only (Option 4).

• Seeds of positively photoblastic species (such as lettuce Lactuca sativa, wild oats, and gladiolus cormels) require red light to convert $P_r$ to active $P_{fr}$ to trigger germination.
• In commercial seed testing and agricultural practice (endorsed by ISTA), Potassium nitrate ($\text{KNO}_3$, 0.1–0.2%) and Thiourea (0.5–1%) are the two most standard non-hormonal chemical agents widely employed to substitute for light requirement and break seed dormancy in dark-incubated seeds.
• Potassium nitrate promotes pentose phosphate pathway oxidation, while thiourea neutralizes germination inhibitors.
• Hence, the most commonly used chemicals to break light-requiring dormancy are (A) Potassium nitrate and (C) Thiourea (Option 4).

Chemicals for breaking seed dormancy:

• Potassium nitrate ($\text{KNO}_3$, $0.2\%$) and Thiourea ($0.5-3\%$) are the standard, officially recommended chemicals (ISTA rules) used to substitute for light requirements and break dormancy in photodormant seeds (like lettuce, oats, gladiolus corms, tobacco).
• Potassium nitrate stimulates the pentose phosphate pathway, while thiourea overcomes inhibition by seed coat phenolics and abscisic acid.
• NAA is a synthetic auxin used for rooting and fruit set, not for breaking photodormancy.