Based on the properties of elements in the periodic table, arsenic (As) is generally considered the weakest conductor of electricity among the given options. While francium (Fr) is an alkali metal and typically has good conductivity, it is highly radioactive and not often encountered in its elemental form for practical conductivity comparisons. Cerium (Ce) and nickel (Ni) are both metals that conduct electricity better than arsenic. Thus, the correct response is:
arsenic (As).