Metal hydrides are ionic, covalent or molecular in nature. Among LiH, NaH, KH, RbH, CsH, the correct order of increasing ionic character is

1.  LiH > NaH > CsH > KH > RbH

2.  LiH < NaH < KH < RbH < CsH

3.  RbH > CsH > NaH > KH > LiH

4.  KH < NaH < RbH < LiH < CsH