Which among the following elements has only one electron in the valence shell?

The hydroxides and carbonates of sodium and potassium are easily soluble in water,while the corresponding salts of magnesium and calcium are sparingly soluble in water. Explain.

The element which cannot form peroxide is

How does the ionization energy of Group $1$ elements change down the group?

Lithium aluminium hydride can be prepared from the reaction of

$A$ metal when left exposed to the atmosphere for some time becomes coated with green basic carbonate. The metal in question is