In my lab report, we are required to explain the trends in solubility of group 2 salts, going down the group. I had explained all of the trends except one, group 2 nitrates. The following is the data provided.
$\ce{Mg(NO3)2}$ – $\pu{0.49 mol}$ per $\pu{100 g}$ of water
$\ce{Ca(NO3)2}$ – $\pu{0.62 mol}$ per $\pu{100 g}$ of water
$\ce{Sr(NO3)2}$ – $\pu{0.16 mol}$ per $\pu{100 g}$ of water
$\ce{Ba(NO3)2}$ – $\pu{ 0.04 mol}$ per $\pu{100 g}$ of water
So as the data shown, the solubility first increases and then decreases. My speculation is that the general trend should decrease but $\ce{Ca(NO3)2}$ has some special properties which makes it more soluble or $\ce{Mg(NO3)2}$ has some special which makes it less soluble. I searched the internet and all I got is "All group 2 nitrates are soluble" with no explanation regarding the trend.
Please correct my speculations if they're wrong and also provide an explanation regarding this trend.