Final answer:
The minimum cation-to-anion radius ratio for a coordination number of 4 is 0.225.
Step-by-step explanation:
The minimum cation-to-anion radius ratio for a coordination number of 4 is 0.225. This means that the cation's size is about 41.4% to 73.2% of the anion's size. The ratio is calculated by dividing the cation radius by the anion radius.