AP EAMCET Engineering 22 Sep 2020 Shift 1 Paper

According to Fajan's rule, the size of the cations increase down a group and also, the increase in size of an atom increases the ionic molecules formed. Caesium being lowest down the group has most ionic character, followed by rubidium, potassium, sodium and lithium respectively.
LiH<NaH<KH<RbH<CsH.