Which alkaline earth metals are included in the group of elements known for being easily ionized?

The group of alkaline earth metals known for being easily ionized consists primarily of Calcium, Strontium, Barium, and Radium. These elements are found in the second group of the periodic table and are characterized by their tendency to lose electrons easily, forming cations with a +2 charge. They have relatively low ionization energies compared to other elements, which makes the ionization process straightforward and energetically favorable.

While Beryllium and Magnesium are also part of the alkaline earth metals, they tend to have higher ionization energies than Calcium, Strontium, Barium, and Radium. This is primarily due to their smaller atomic sizes and greater effective nuclear charge, which holds electrons more tightly and makes them harder to remove.

In summary, the elements in the correct choice not only belong to the alkaline earth metal group but also are distinguished by their ease of ionization, especially in comparison to the other elements listed in the other choices.