Final answer:
For older adults, performing tasks that demand cognitive function along with physical action can be particularly difficult due to the decline in fluid intelligence, which affects memory, reasoning, and information processing abilities.
Step-by-step explanation:
Particularly difficult for older adults is combining a cognitive task with a physical task. This is because as people age, they begin to experience a decline in fluid intelligence which affects information processing abilities, reasoning, and memory. These processes become slower, and older adults often find it more challenging to perform tasks that require both cognitive and physical engagement.
This can be seen in the difficulty older individuals may have in combining tasks that demand cognitive function, such as planning or problem-solving, with those that require physical action, like balancing or coordinating movements.