What do elements in group 2a have in common in the periodic table?

The alkali metals are lithium, sodium, potassium, rubidium, cesium and francium, and the alkaline earth metals are beryllium, magnesium, calcium, strontium, barium and radium. Hydrogen is placed on the periodic table above group 1a but is not considered part of the group. 
Refer to: https://www.reference.com/.../group-1a-group-2a-elements-common-94c6bc654f3d5a4...

Answerthis solution will not form a precipitateexplanationsolubility equilbrium:         pbf₂(s)  ⇄ pb²⁺(aq) + 2 f⁻(aq)the solubility product expression is    (we exclude solids from the equilibrium expression).now suppose we have the trial ion product q, which we can define as    then, we can interpret  q as the product of the concentration of the ions that we have and ksp as the product of the ion concentrations that are needed to form a saturated solution.if q > ksp, then that implies that there will be a surplus of ions that exceed the amount that is required to form a saturated solution. a precipitate will then form (the precipitate continually  forms until the surplus ions are removed and q is decreased to ksp's value).if q = ksp, the saturated solution that forms is barely saturated and the precipitate will be minimal.if q < ksp, then the ion concentration will not be enough to form a saturated solution (so no precipitate).using our information, we calculate the trial ion product:     since q = 2.7  × 10⁻⁸ < ksp =  4  ×  10⁻⁸, a precipitate will not form.