To determine the correct relationship of beryllium (Be), calcium (Ca), and strontium (Sr) regarding their energy, specifically in terms of their ionization energy, we need to understand how ionization energy changes as you move down a group in the periodic table.
Ionization energy is the energy required to remove an electron from an atom in its gaseous state. For the elements in Group 2 of the periodic table, ionization energy decreases as you move down the group. This is because as you go down the group:
1. The atomic size increases, meaning the outermost electron is further from the nucleus.
2. There is an increase in the number of electron shells, which leads to greater shielding of the outermost electron from the attraction of the nucleus.
Due to these factors, the effective nuclear charge experienced by the outermost electron decreases, and less energy is required to remove it.
Given this understanding, we can order the three elements based on their decreasing ionization energies as follows:
1. Beryllium (Be) has the highest ionization energy because it is at the top of the group.
2. Calcium (Ca) has a lower ionization energy than beryllium but higher than strontium.
3. Strontium (Sr) has the lowest ionization energy of the three because it is further down the group.
Therefore, the correct relationship based on ionization energies is:
[tex]\[ Be > Ca > Sr \][/tex]
To match this with the given options:
A. [tex]$Ca < Be < Sr$[/tex] - This suggests Ca has less energy than Be and Sr has more than both, which is incorrect.
B. [tex]$Sr < Be < Ca$[/tex] - This suggests Sr has less energy than Be and Ca has more than Be, which is incorrect.
C. [tex]$Be < Ca < Sr$[/tex] - This suggests Be has less energy than Ca and Sr, which is incorrect.
D. [tex]$Sr < Ca < Be$[/tex] - This suggests Sr has less energy than Ca, and Ca has less energy than Be, which aligns correctly with the trend.
E. [tex]$Ca < Sr < Be$[/tex] - This suggests Ca has less energy than Sr and Be has more energy than both, which is incorrect.
Thus, the correct answer is:
[tex]\[ \boxed{D} \][/tex]
