Q.In a fully turgid cell

Step 1. For any plant cell, Diffusion Pressure Deficit follows DPD = OP − TP, where OP is osmotic pressure and TP is turgor pressure.

Step 2. A cell is defined as fully turgid only when it has absorbed the maximum water its wall's elastic limit allows - at that point the outward-pushing osmotic pull is exactly balanced by the wall's inward turgor pressure, so OP = TP.

Step 3. Substituting OP = TP into DPD = OP − TP gives DPD = 0 for any fully turgid cell, whatever the actual numeric value of OP and TP, so long as the two are equal.

Step 4. Checking each option against this rule: option (a) gives DPD = 10 while OP (5) ≠ TP (10), which is internally inconsistent; option (c) claims DPD = 0 but OP (5) ≠ TP (10), which is also inconsistent, since DPD can only be zero when OP and TP are equal; option (d) gives OP = TP = 20, not the stated TP of 10, and a nonzero DPD despite OP = TP, another contradiction. Only option (b) has OP = TP = 10 atm and the matching DPD = 0.

Apply DPD = OP − TP together with the fully-turgid-cell condition OP = TP, and test each option for internal consistency.

• Assuming DPD is always a large positive number and missing that it becomes zero specifically at full turgidity.
• Picking an option purely because DPD = 0 is stated, without checking that OP and TP are actually equal to each other.