Answer: Br
Explanation:
![Br:35:[Ar]3d^(10)4s^24p^5](https://img.qammunity.org/2017/formulas/chemistry/high-school/jlnkgg6qusu7vihgrzqqgtb4v5i60h5195.png)
![Br^-:36:[Ar]3d^(10)4s^24p^6:[Kr]](https://img.qammunity.org/2017/formulas/chemistry/high-school/nrkb9xbnmgf1mbf78r8lapvfow20esbzac.png)
![Na:11:[Ne]3s^1](https://img.qammunity.org/2017/formulas/chemistry/high-school/iht69gbgef76bopu9pnb2hiebg0n0hdgim.png)
![Na^-:12:[Ne]3s^2](https://img.qammunity.org/2017/formulas/chemistry/high-school/ktul8g6p85dbtj3ro4zyn3no2b5inpyqvi.png)
![Al:13:[Ne]3s^23p^1](https://img.qammunity.org/2017/formulas/chemistry/high-school/ihxkwmw16iy1jo0j9k0bcc08cir7j5o1jo.png)
![Al^-:14:[Ne]3s^23p^2](https://img.qammunity.org/2017/formulas/chemistry/high-school/kxlrldm8gqqnyae7tghpkhzh9c8hlcatjl.png)
![S:16:[Ne]3s^23p^4](https://img.qammunity.org/2017/formulas/chemistry/high-school/wjqfd1jry0z64n8tvurzm3h87qxo4kolc8.png)
![S^-:17:[Ne]3s^23p^5](https://img.qammunity.org/2017/formulas/chemistry/high-school/y5f4chue67x1pl7ps80gu7y9kedp9w5t34.png)
As Bromine is short of only 1 electron to attain noble gas configuration, it will release energy as more stable species have less energy. Thus bromine would release most energy while adding an an electron to a neutral atom in the gas phase.
All other species Na, Al and S would not attain stable configuration on addition of electron and hence no energy would be released.