Question

The reactivity of $Ca,{\text{ }}Sr,Mg{\text{ }}and{\text{ }}Ba$ with water follows the order:
A: $Sr > Ba > Mg > Ca$
B: $Ba > Sr > Ca > Mg$
C: $Ca > Mg > Ba > Sr$ $- {\rm I}{\rm I}$
D: $Sr > Ca > Mg > Ba$

Answer 1

Every order of reactivity and the chemical properties of different compounds follow some order according to the trends of the periodic table. May be along the group or may be along the period which we have to judge according to the question in this question we can see all the elements are of the same group.

Complete step by step answer:
In this question elements given are calcium $Ca$ , strontium $Sr$ , magnesium $Mg$ and barium $Ba$ . Which are members of the same group that is Group which are also called alkaline earth metals.
As we go down the group number of shells in an atom increases due to which size of the atom also increases. This means the distance between nucleus and valence electrons increases and hence the attractive force between nucleus and outermost electron decreases also there is more shielding down the group which promotes the same and the cation formed from the elements are more stable and gives faster reaction with water to form hydroxides. Our order for the reactivity of $Ca,{\text{ }}Sr,Mg{\text{ }}and{\text{ }}Ba$ with water follows the pattern down the group which is as:
$\ Mg - Group - 2,Period - 3 \\\ Ca - Group - 2,Period - 4 \\\ Sr - Group - 2,Period - 5 \\\ Ba - Group - 2,Period - 6 \\\ \$

Hence our answer to this question will be option B that is $Ba > Sr > Ca > Mg$.

Note:
It is point to be noted that Beryllium $\left( {Be} \right)$ is also part of this Group$- {\rm I}{\rm I}$ alkaline earth metals and it is the top of the element in that group according to trend (reaction of group two elements with water) it should be least reactive but this element does not react with water at normal conditions.