Assertion $(A)$: van der Waals' forces are responsible for chemisorption.
Reason $(R)$: High temperature is favourable for chemisorption.
The correct answer is

• A
  $(A)$ is false, but $(R)$ is true
• B
  Both $(A)$ and $(R)$ are correct and $(R)$ is the correct explanation of $(A)$
• C
  Both $(A)$ and $(R)$ are correct and $(R)$ is not the correct explanation of $(A)$
• D
  $(A)$ is true, but $(R)$ is false