Final answer:
Memory recall is the ability that relies most on crystallized intelligence because it involves accessing and leveraging previously acquired knowledge.
Step-by-step explanation:
The ability that involves crystallized intelligence to the greatest extent is memory recall. Crystallized intelligence is characterized by the knowledge you acquire over time and your ability to retrieve it. This form of intelligence is relied upon when learning, remembering, and recalling information. For example, when you demonstrate mastery of course material or when older adults show stable to increasing scores on intelligence tests, they are using crystallized intelligence. On the other hand, fluid intelligence is the ability to see complex relationships and solve problems.
When assessing options like speed of processing, this is more associated with fluid intelligence and information processing abilities. Spatial reasoning, while it can draw on previously learned information, often requires fluid intelligence to solve novel spatial challenges. Therefore, the correct answer is memory recall, as it relies heavily on the retrieval of previously learned information which is at the core of crystallized intelligence.