see we want our genetic material to be stable may under go mutations not much reactive
so now let's see
dna is comparatively more stable than rna because in rna is an OH- group which makes it unstable so from here we conclude that dna might be genetic material
now next
dna under goes less mutations to than rna
moreover rna is very reactive and rna also acts us catalst in many rxns so dna is comparatively less reactive
and due to all these pts. we may say dna is the genetic material not rna