(a). Which alkaline earth metals do not give characteristic colour to the Bunsen flame?
(b). Why alkaline earth metals do not form tripositive ions?
(c ). Why alkaline earth metals are diamagnetic, but alkali metals are paramagnetic?
(d). Why the first inonisation enthaply pf alkaline earth matals is higher than those of corresponding alkali metals?
(e). Why alkaline earth metals are less electropositive than corresponding alkali metals?

Explanation

a. `Be` and `Mg` do not give characteristic colour to the bunsen flame.
B. General electronic configuration of alkaline earth metals is `ns^(2)` preceded by noble gas core. After the removal of two electrons, bipositive cation formed acquires a stable noble gas configuration. for the removal of the third electron, a very large amount of energy is required and that is why alkaline earth metlas do not form tripositive ion, `M^(3+)`.
`underset(2p^(6)3s^(2))(Mg)overset(IE_(1))underset(-e^(Θ))(rarr)underset(2p^(6)3s^(1))(Mg^(o+))overset(IE_(2))underset(-e^(Θ))(rarr)underset(2p^(5)3s^(0))underset(Mg^(3+))underset(-e^(Θ)darrIE_(3))underset("Stable noble gas configuration")underset(2p^(6)3s^(0))(Mg^(2+))`
c. In case of alkaline earth metals, the general electronic configuration is `ns^(2)`. Due to the presence of paired electons in their atoms, alklaline earth metals are diamagnetic. In case of alkali metals, general electronic configuration is `ns^(1)`. Due to the presence of unpaired electron, alklai metals are paramagnetic.
d. Alkaline earth metals have smaller size as compared to corresponding alkali metals due to increases charge, as a result the higer amount of energy is required for the removal of an electorn from the valence shell. that is why the first ionisation enthalpy of alklaline earth metal is higher than the corresponding alklai metal.
e. Alkaline earth metals have smaller size as compared to alkali metals. Hence, valence shell electrons are more tightly bound to the nucles and ionisation entyhalpy of alkaline earth metals is more is more as compared to alkali metals. consequently, they have less tendency to lose valence shell electrons and are less electropositive as compared to alkali metals.