The alkaline earth metal nitrate that does not
crystallise with water molecules, is :
(1) Sr(NO3)2 (2) Mg(NO3)2
(3) Ca(NO3)2 (4) Ba(NO3)2

Always remember this thing that “smaller the size of cental atoms more  the water molecules will crystallize” hence Ba(NO3)₂ is the answer due to its larger size of '+ve' ion.