Explain why it is easier to predict the atomic radius of radium then the melting point of radium ?

please mark me as brainliest

Radium was discovered in 1898 by Marie Curie and Pierre Curie. They managed to extract 1 mg of radium from ten tonnes of the uranium ore pitchblende (uranium oxide, U3O8), a considerable feat, given the chemically methods of separation available to them. They identified that it was a new element because its atomic spectrum revealed new lines. Their samples glowed with a faint blue light in the dark, caused by the intense radioactivity exciting the surrounding air.

i just calculated it all out, and not including weekends, and all the different days off. as of this school year (2018-2019) students are spending 2198 hours in school this year