1) Answer is: the elements of group 17 (or group 7A) in the periodic table release the most energy by gaining an electron.
Group 17 (halogens) elements are in group 17: fluorine (F), chlorine (Cl), bromine (Br) and iodine (I). They are very reactive and easily form many compounds.
Halogens need to gain one electron to have electron cofiguration like next to it noble gas. For example, fluorine has 9 electrons and it gain easily one electron in chemical reaction to have electron configuration like noble gas neon (Ne) with 10 electrons.
2) Answer is: elements of group 18 (or group 8A) in the periodic table absorb the most energy when gaining an electron.
Noble gases (group 18) are in group 18: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn). They have very low chemical reactivity.
Noble gases have very stable electron configuration and does not need to gain electrons, only when they gain energy.
