Assertion (A) : The Monarch butterfly is highly distasteful to the predators. Reason (R) : The butterfly has a very rough skin which is not palatable.

The correct option is: Assertion (A) is true, but Reason (R) is false.

Step-by-step Explanation:

1. Analyzing the Assertion (A):
The assertion states: "The Monarch butterfly is highly distasteful to the predators."
This statement is biologically accurate. The Monarch butterfly (Danaus plexippus) is well-known for being extremely distasteful and toxic to its predators, particularly birds. When a predator attempts to eat a Monarch butterfly, it experiences severe chemical irritation or vomiting, which teaches the predator to avoid this butterfly species in the future. Thus, Assertion (A) is true.

2. Analyzing the Reason (R):
The reason states: "The butterfly has a very rough skin which is not palatable."
This statement is scientifically incorrect. The distasteful nature of the Monarch butterfly is not due to any physical texture or "rough skin." Instead, it is due to a chemical defense mechanism. During its caterpillar stage, the Monarch feeds on milkweed plants (genus Asclepias). Milkweed contains toxic chemicals called cardiac glycosides (cardenolides). The caterpillar sequesters (stores) these toxins in its body, and they remain in its tissues even after it metamorphoses into an adult butterfly. It is these chemical cardiac glycosides that make the butterfly highly distasteful and poisonous to predators, not its skin texture. Thus, Reason (R) is false.

Conclusion:
Since Assertion (A) is true but Reason (R) is false, the correct choice is "Assertion (A) is true, but Reason (R) is false."