(A]: Cytokinins help in retention of chlorophyll and delayed senescence in leaves.
[R]: Cytokinins only stimulate root initiation

Options

A. (a) If both A and R are true and R is the correct explanation of A
B. (b) If both A and R are true but R is not the correct explanation of A
C. (c) If A is true and R is false
D. (d) If both A and R are false

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that "Cytokinins help in retention of chlorophyll and delayed senescence in leaves."
- Cytokinins are a class of plant hormones that play a significant role in promoting cell division and growth. They are known to delay the aging process (senescence) in plants by helping to retain chlorophyll, which is essential for photosynthesis.

2. **Analyzing the Role of Cytokinins**:
- Cytokinins promote the retention of chlorophyll in leaves, which keeps them green and healthy. This is crucial because chlorophyll is responsible for the green color of leaves and is vital for photosynthesis.
- When chlorophyll is retained, the leaves can continue to produce food for the plant, thus delaying the aging process.

3. **Understanding the Reason**: The reason states that "Cytokinins only stimulate root initiation."
- This statement is incorrect. While cytokinins do play a role in plant growth, they are primarily associated with promoting shoot development and cell division rather than root initiation. Root initiation is primarily stimulated by another hormone called auxin.

4. **Conclusion**:
- Since the assertion is true (cytokinins do help in retaining chlorophyll and delaying senescence), but the reason is false (cytokinins do not only stimulate root initiation), we conclude that the correct answer is that the assertion is true and the reason is false.

5. **Final Answer**: The correct option is C: Assertion is true, but reason is false.