Answer:
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Step-by-step explanation:
Radium (Ra) is an element in Group IIA/2 of the periodic table, which is also known as the alkaline earth metals group. Given the atomic radius, density, and melting point values for neighboring elements in this group (strontium Sr and barium Ba), we can make reasonable predictions for the missing values for radium (Ra).
Atomic Radius: The atomic radius generally increases as you move down a group in the periodic table because additional electron shells are added. So, we would expect the atomic radius of radium (Ra) to be larger than that of barium (Ba). Therefore, a reasonable estimate for the atomic radius of radium (Ra) could be around 219-220 pm.
Density at 20°C: The density of elements in Group IIA/2 also tends to increase as you move down the group due to increased atomic mass. Given that strontium (Sr) has a density of 2.63 g/mL and barium (Ba) has a density of 3.65 g/mL, it is reasonable to predict that radium (Ra) would have a higher density than barium. A reasonable estimate for the density of radium (Ra) could be around 4.0-4.5 g/mL.
Melting Point: The melting point of elements in Group IIA/2 can vary, but it often decreases slightly as you move down the group. Given that strontium (Sr) has a melting point of 769 °C and barium (Ba) has a melting point of 725 °C, it is reasonable to predict that radium (Ra) would have a melting point somewhat lower than that of barium. A reasonable estimate for the melting point of radium (Ra) could be around 700-720 °C.
Please note that these are rough estimates based on trends in the periodic table, and actual experimental values for radium may vary.