Answer:
It is longer than a solar eclipse
Density * Volume = Mass
Now we substitute the values in.
19.3 g/cm^3 + 20 cm^3 = 386 g
Mass = 386 g
The atomic number of Be is 4, and so it has 2 shells. There are valence electrons in the second, which is the outermost, shell of Be. To get the element with one more shell, there would be 3 shells on the new element, and 1 less valence electron, so the new element should have 1 valence electron. Sodium is the element with 3 shells, and one valence electron which fits perfectly into the description.
