There's two ways to answer this question.
First electron configurations with half-filled sublevels are more stable then electron configurations that don't have half-filled sublevels. Since Selenium is one elctron away from achieving a more stable half-filled sublevel configuration it more readily gives up it's outermost electron, so less energy is requires to remove the outermost electron. Arsenic already has the stable configuration of half-filled sublevel so it wouldn't give up it's electron as readily, so more energy is required to remove it.
Another way to look at it is that Selenium's outermost electron is in a p orbital that already has an electron so there is electron electron repulsion present in that orbital so it's attraction to the nucleus is less which is why less energy is required to remove it so the ionization energy is less. Arsenic has it's outermost electron unpaired in the p orbital so there is no electron electron repulsion present in that orbital so more energy is required to remove it then for Selenium's outer most electron.
Hope this helps!
Arsenic is closer to having a full outer electron shell ( AKA noble gas configuration) , thus it does not want to give up any of its electrons. Germanium is not as close.
Selenium has the greater electron affinity
Bromine, its as simple as its more to the RHS of the periodic table
Oxygen (1313,9 kJ/mol) has a greater ionzation energy than lithium (520,2 kJ/mol).
germanium has greater mass and thus is harder to move
First ionization energy is the energy required to remove the first outermost electron from an atom. The second ionization energy is the energy required to remove the next available electron, and is greater than the first IE. The third IE is that energy needed to remove the third electron, and is greater the the second IE.
Beryllium has greater ionization energy, with 899 kJ/mol versus Germanium's 762 kJ/mol. The general trend (most prominently displayed in the representative elements) in the periodic table is increasing ionization energy across a period, and decreasing ionization energy down a group.
potassium is greater in the second ionization energy.
sodium because it's the first group and first group are the most
because its size is big and hence have greater tendency to accept electrons.
kwana warkawa
because it lower than Ba as you go down ionization energy increases
Selenium has the greater electron affinity
Though germanium diodes were the first ones fabricated, several factors make silicon the choice vs. germanium diodes. Silicon diodes have a greater ease of processing, lower cost, greater power handling, less leakage and more stable temperature characteristics than germanium diodes. Germanium diodes' lower forward drop (.2V to .3V versus .7V to 1.0V) make them better at small signal detection and rectification.
Lithium
With greater ionization energy, nonmetals have greater reactiveness. This is because they don't want to lose electrons at all! They will instead gain electrons to complete the octet.This proves true in the element Fluorine.
Bromine, its as simple as its more to the RHS of the periodic table
Neon is a much smaller atom than selenium because neon has fewer occupied energy levels so it has a considerably smaller atomic radius. For that reason, it will be more difficult to remove an electron from Ne than Se, so Ne has the greater ionization energy.