Which of the following statements is false?

1. A
   ${\text{Ca}}^{2+}$ ions are important in blood clotting.
2. B
   ${\text{Ca}}^{2+}$ ions are not important in maintaining the regular beating of the heart.
3. C
   ${\text{Mg}}^{2+}$ ions are important in the green parts of plants.
4. D
   ${\text{Mg}}^{2+}$ ions form a complex with $\text{ATP}$.