If a dried cobalt chloride paper is clipped on the under surface of a leaf, its colour changes from blue to pink because

Options

A. it reacts with the chlorophyll of the leaf
B. the clipper puts a pressure on the paper
C. paper is moistened by the transpiring water
D. it comes in contact with green leaf

Answer

To answer the question about why the color of dried cobalt chloride paper changes from blue to pink when clipped on the under surface of a leaf, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Cobalt Chloride Paper**: Cobalt chloride paper is a chemical indicator that is blue when dry and turns pink when it comes into contact with water. This property is crucial for our understanding of transpiration.

2. **Transpiration Process**: Transpiration is the process by which water vapor is lost from the aerial parts of plants, primarily through small openings called stomata, which are mostly found on the underside of leaves.

3. **Clipping the Paper to the Leaf**: When the cobalt chloride paper is clipped to the underside of a leaf, it is positioned to detect any moisture that may be released from the leaf due to transpiration.

4. **Moisture Transfer**: As the plant transpires, water vapor is released into the air. Some of this water vapor can condense on the cobalt chloride paper, causing it to absorb moisture.

5. **Color Change**: When the cobalt chloride paper absorbs water from the transpiration process, it changes color from blue to pink, indicating that moisture is present.

6. **Conclusion**: Therefore, the color change from blue to pink signifies that transpiration is occurring, as the paper is moistened by the water vapor released from the leaf.

### Final Answer:
The color of the dried cobalt chloride paper changes from blue to pink because it is moistened by water vapor released during transpiration from the leaf.