In Streptococcus pneumoniae

Below experiment of

Chemically $DNA$ differs from $RNA$ in having

Which property of $DNA$ double helix led Watson and Crick to hypothesise semiconservative mode of $DNA$ replication? Explain.

During the course of evolution why $DNA$ was chosen over $RNA$ as genetic material ? Give reasons by first discussing the desired criteria in a molecule that can act as genetic material and in the light of biochemical differences between $DNA$ and $RNA$.