In 6.298 moles of Mg²⁺ ions, there are approximately 3.797 x 10^24 Mg²⁺ ions. This calculation is done by using Avogadro's number, which states that there are approximately 6.022 x 10^23 entities (in this case, ions) in one mole of a substance. So, 6.298 moles of Mg²⁺ ions would contain 6.298 x 6.022 x 10^23 ions.