Answer:
Br
Step-by-step explanation:
The first ionization energy is a measure of the energy required to remove the outermost, or highest energy, electron from an atom or a positive ion. Among the elements Na, P, Ca, and Br, the element with the highest first ionization energy is Br.
The first ionization energy generally increases across a period (row) on the periodic table and decreases down a group (column). This trend is due to the increasing effective nuclear charge (the positive charge felt by an electron) and decreasing electron shielding (the effect of inner electrons on the energy of outer electrons) as one moves from left to right across a period.
In the case of Na, P, Ca, and Br, all four elements are in the same period, so they experience similar effective nuclear charge. However, Br has a higher atomic number than the other three elements, which means it has more protons in its nucleus and a stronger positive charge. This leads to a higher first ionization energy for Br compared to Na, P, and Ca.
Overall, the element with the highest first ionization energy among Na, P, Ca, and Br is Br.