The transpiration from the two leaf surface are compared by dry paper strips previously dispatched in solution
A. Sodium Chloride
B. Cobalt
C. Cobalt chloride
D. Calcium chloride

Hint: The evaporation of water from the plant is known as transpiration. Water is transported through the xylem column from the soil to the other parts of plants but plants use very small amounts of water for their growth and development. A maximum amount of water is lost during transpiration.

Step by step answer:The comparison of transpiration between two leaf surfaces means the comparison of the rate of transpiration of leaves. For comparison between leaves rate of transpiration, the leaves are soaked in the cobalt chloride solution and after when the solution becomes dry the cobalt chloride strip becomes blue, when the transpiration starts the cobalt chloride strips on the leaves change colour. The cobalt strips attached to leaves change colour from blue to pink. Cobalt chloride changes its colour when it comes in contact with water. The dry cobalt chloride is blue in colour and wet cobalt chloride is pink in colour. Hence when leaves undergo transpiration the blue strip changes into pink. We can compare the rate of transpiration by comparing the time taken for the strip to change its colour from blue to pink.
So, the correct option is C
Additional Information: Leaves and green parts of the plant contain tiny pores known as stomata. These pores open during light and facilitate water evaporation. The number of stomata, size of stomata, and type of stomata vary from plant to plant. The upper part of the plant and the lower part of the plant may vary in the number of stomata within the plant. Therefore every plant has a different rate of respiration.

Note: Advantage of Transpiration:
1. In long tress the water transport from the soil in the other parts of trees by the transpiration pull.
2. On hot days transpiration helps plants to maintain their temperature.
3. Transpiration also plays an important role in maintaining the water cycle. It helps to increase water vapour in the air.