It is very easy to obtain `M^(+)` ion from an atom of alkaline earth metals. But `M^(+)` ions are not formed. Why? 

Explanation

Though the formation of `M^(+2)` ions is difficult, alkaline earth metals are familier to have them in solid state as well as in solution state. The lattice energy in solid state or hydration energy in solutions of `M^(2+)`  ions is more. This dominates the second ionisation energy of alkalinc carth metals.