To determine the coagulating power of an ion, we need to consider the factors that influence it.$\\$The coagulating power of an ion is related to its ability to neutralize the charge on colloidal particles, leading to coagulation.$\\$According to the Hardy-Schulze rule, the coagulating power of an ion depends on:$\\$• The magnitude of the charge on the ion: Higher charge leads to greater coagulating power.$\\$• The sign of the charge on the ion: The ion must have a charge opposite to that of the colloidal particles to neutralize them.$\\$Therefore, both the magnitude and the sign of the charge on the ion are important.$\\$Let's analyze the options:$\\$Option 1: Both magnitude and sign of the charge on the ion$\\$This option is correct because both factors are crucial for coagulation.$\\$Option 2: Size of the ion alone$\\$This is incorrect because the size of the ion does not directly influence coagulating power.$\\$Option 3: The magnitude of the charge on the ion alone$\\$This is partially correct, but it ignores the importance of the sign of the charge.$\\$Option 4: The sign of charge on the ion alone$\\$This is partially correct, but it ignores the importance of the magnitude of the charge.$\\$Thus, the correct answer is Option 1: Both magnitude and sign of the charge on the ion.