The electron configuration that belongs to the atom with the lowest first ionization energy is francium.
<h3>What is ionization energy? </h3>
Ionization energy is defined as the minimum amount of energy required to remove the most loosely electron present in outermost shell.
<h3>Ionization energy across period</h3>
Ionization energy increase as we move from left to right in the period. This can be explained as when we move from left to right along period new electron is added to the same shell which increase the nuclear charge. Hence results int he decrease in size. Due to this decrease in size more energy is required to remove electron from outermost shell.
<h3>Ionization energy along group</h3>
Ionization energy decrease as we move from top to bottom along group. This can be explained as we move from top to bottom new electron is added to new shell. Due to addition of new shell the size of atom increases which results in the decrease in the nuclear charge. Due to this less amount of energy is needed to remove an electron.
Thus, we concluded that the electron configuration that belongs to the atom with the lowest first ionization energy is francium.
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