Final answer:
The statement that describes the relationship between Alejandra's initial acceleration vector and her vector after ten minutes is that her later acceleration is in the opposite direction of her initial velocity, as she is slowing down.
Step-by-step explanation:
The question concerns a change in velocity and therefore acceleration vectors in a real-world scenario, which is a fundamental concept in Physics. Alejandra is initially riding her bike at a rate of 10 km/hr and then slows down to 8 km/hr after ten minutes. The statement that best describes the relationship between her initial acceleration vector and the acceleration vector after ten minutes is that her acceleration vector after ten minutes must be in the direction opposite to her initial velocity if her speed is decreasing. Without numerical details about the duration of the change in speed, we cannot provide the exact value of acceleration.