Transpiration highest with low humidity and high temperature

Steps:

• Transpiration rate increases as humidity decreases due to steeper water vapor gradient from leaf to air.
• Transpiration rate increases with temperature as it boosts evaporation and diffusion kinetics.
• Evaluate humidity: 60% (A, B) allows higher rate than 100% (C, D).
• Evaluate temperature: 25°C (B, C) allows higher rate than 15°C (A, D); B combines lowest humidity and highest temperature.

Why B is correct:

• B features 60% humidity (steep gradient per Fick's law of diffusion) and 25°C (elevated evaporation rate), maximizing transpiration.

Why the others are wrong:

• A: Lower temperature (15°C) reduces evaporation compared to B.
• C: High humidity (100%) minimizes vapor gradient, halting transpiration.
• D: High humidity (100%) and low temperature (15°C) both suppress transpiration.

Final answer: B