I am one of the elements. I am a metal that can form a cation. My atomic number is Z. My atomic radius is smaller than the atomic radius of the element Z-1 but is larger than the atomic radius for Z-2. Of the two elements in my group that have biological importance, I am the one with lower atomic mass. Who am I

Beryllium

Explanation:

From the information given: Beryllium has the ability to form a monoatomic divalent metal cation. The atomic number (Z) is 4 and the mass number is 9. The atomic element of (Z-1) is Li and that of (Z-2) is He. The elements they are referring to that share the same similar biological importance within Beryllium are Magnesium and Calcium because they are in the same group.

The atomic radii of He = 140

The atomic radii of Li = 182; &

The atomic radii of Be = 153 pm

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