What is the halide ion?

A compound is known to be a potassium halide,KX . If 3.00 g of the salt is dissolved in exactly 100 g of water, the solution freezes at –1.92 °C. Identify the halide ion in this formula. Kfp for H2O is –1.86 degrees celsius over m
Update: I put the answer to be F because that's what i got and it marked it wrong so idk
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