Which of the following is the correct order of basic strength?

As the alkaline earth metals (except $Be$) tend to lose their valence electrons readily,they act as:

Which one of the following pairs does not impart colour to the flame?

The correct order of density for the alkaline earth metals is:

The most basic among these hydroxides is:

How would you explain the following observations?
$(i)$ $BeO$ is almost insoluble but $BeSO_4$ is soluble in water,
$(ii)$ $BaO$ is soluble but $BaSO_4$ is insoluble in water,
$(iii)$ $LiI$ is more soluble than $KI$ in ethanol.