Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs), and Francium (Fr) are in the same column in the periodic table. Why are these elements in the same column in the periodic table?

Asample of hydrated tin (ii) chloride (sncl2) has a mass of 4.90 g. when it is dehydrated, it has a mass of 4.10 g. which is the correct chemical formula for the hydrate? sncl2•2h2o          sncl2•4h2o          sncl2•6h2o