To solve this problem, we need to evaluate each statement and determine which one is false.$\newline$Let's analyze each option:$\newline$• Option 1: $Mg^{2+}$ ions form a complex with ATP.$\newline$ - This statement is true. $Mg^{2+}$ ions are known to form complexes with ATP, which is important for many biological processes.$\newline$• Option 2: $Ca^{2+}$ ions are important in blood clotting.$\newline$ - This statement is true. $Ca^{2+}$ ions play a crucial role in the blood clotting cascade.$\newline$• Option 3: $Ca^{2+}$ ions are not important in maintaining the regular beating of the heart.$\newline$ - This statement is false. $Ca^{2+}$ ions are essential for cardiac muscle contraction and help maintain the regular beating of the heart.$\newline$• Option 4: $Mg^{2+}$ ions are important in the green parts of plants.$\newline$ - This statement is true. $Mg^{2+}$ ions are a central component of chlorophyll, which is vital for photosynthesis in plants.$\newline$Therefore, the false statement is Option 3.