Solution:
Option (ii) is the answer.
As we advance down the group, the ionic nature rises. As ionisation enthalpy drops from top to bottom in a group, metal tends to lose electron. So ionic character grows.
Metal hydrides are ionic, covalent or molecular in nature. Among LiH, NaH, KH, RbH, CsH, the correct order of increasing ionic character is (i) LiH > NaH > CsH > KH>RbH (ii) LiH < NaH < KH < RbH CsH > NaH > KH > LiH (iv) NaH > CsH > RbH > LiH > KH