Among the provided options, the most notable disadvantage of using a functional language is:
"It’s more difficult to execute many operations at the same time."
Functional languages often emphasize immutability and state management, which can make parallelization and concurrent execution more complex compared to imperative languages. However, it's worth noting that many functional languages have strong support for concurrency, but the model of execution and reasoning about side effects can be more challenging in practice.
Other statements could also be argued in certain contexts, but this particular point stands out in discussions about the challenges of functional programming.