Final answer:
The electron lost when indium (In) forms a cation is from its outermost energy level. Indium's configuration is [Kr]4d10 5s2 5p1, therefore, the electron in 5p1 is lost first, making the correct answer C) 5p1.
Step-by-step explanation:
The student has asked which electron in the electron configuration of indium (In) will be lost when it forms a cation. Looking at the general properties of element cations formation, main group element cations tend to lose the electrons added last to their electron configuration. Indium falls into this category and not among the transition or inner transition metals.
Indium has the electron configuration [Kr]4d105s25p1. When indium forms a cation, it will lose electrons starting from the highest energy level, which is the outermost shell. Therefore, the electron lost to form an In+ ion will be the 5p1 electron.
The correct answer is C) 5p1. Electrons from the s orbital are not usually lost before the p orbital in main group elements, and d and f electrons are even less likely to be lost due to their lower energy levels in comparison to the last added electrons.