The problem above is simply asking to convert one unit of energy to another of unit energy. We convert measurements by multiplying conversion factors. The conversion factor, for this case, is 1 cal / 4.184 kJ. We multiply this value to the measurement.
If it is located at the second to last row of the periodic table (the halogen family), has seven electrons on it's outer shell, and has an oxidation number of -1, it is a halogen. Hope this helps : D
