Replication was allowed to take place in the presence of radioactive deoxynucleotides precursors in $\rm {E. coli}$ that was a mutant for $\rm {DNA}$ ligase. Newly synthesised radioactive $\rm {DNA}$ was purified and strands were separated by denaturation. These were centrifuged using density gradient centrifugation. Which of the following would be a correct result
$(d)$
Write short note on $RNA$ World.
Identify the incorrect statement about $RNA.$
$A$ : Catalytic functions were assigned to $RNA$ molecule during evolution.
$R$ : The rate of mutation is quite fast in $RNA$
Describe in short about $RNA.$