Final answer:
When arranging the elements in order of decreasing first ionization energy, the correct order is Cl, Se, Te, and Po.
Step-by-step explanation:
When arranging the elements in order of decreasing first ionization energy, we need to consider the trends in ionization energy across the periodic table. Ionization energy generally increases from left to right in a period and decreases from top to bottom in a group. Based on this, we can arrange the elements as follows:
- Cl
- Se
- Te
- Po
Therefore, the correct order of the elements from highest to lowest first ionization energy is Cl, Se, Te, and Po.