Question

Which element of group $-2$ is not considered as an alkaline metal?

Answer 1

Hint: Consider the amphoteric behaviour of different elements in group $2$ different element in the group as one of them shows this behaviour. An amphoteric compound is a molecule or ion capable of reacting as an acid and as a substrate. Many metals contain amphoteric oxides or hydroxides (such as copper, zinc, silver, brass, aluminium, and beryllium).

Complete answer:
In periodic table alkaline earth metals are at the second group they are six elements in group\[2\] which are named as beryllium $Be$, magnesium\[Mg\], calcium \[Ca\], strontium\[Sr\], barium\[Ba\] and radium\[Ra\]. They contain similar physical properties like they all are shiny and have silvery-white appearance somewhat their chemical properties are also similar as they are reactive metals at standard temperature and pressure.
As these elements are also known as alkaline earth metals except beryllium, the reason that they are called alkaline earth metal because their oxides exist in earth’s crust also they are very stable to heat that why we use the word earth here and one more reason that they are called alkaline earth metals is because their oxides and hydroxides show basic natures or we can say alkaline nature.
As beryllium fulfils the first criteria of existing oxides and is found in earth’s crust but it is unable to fulfil the second criteria since its oxides and hydroxides show amphoteric behaviour, rather than alkaline.
So beryllium is not considered as alkaline earth metal even after it does resemble a lot in various other properties with them.

Note:
In periodic table we consider amphoteric behaviour where some species which we consider here as molecule or ions which can act as both acid and base, here we can see the example of beryllium other examples can be zinc and lead.