The $T_4$ bacteriophage $rII$ mutant strain fails to lyse $E. coli$. However,when two strains $rII^X$ and $rII^Y$ are mixed,they lyse $E. coli$. What is the possible reason for this?

Match the following columns:

Column-$I$	Column-$II$	Column-$III$
$(1) \ 1952$	$(a)$ Watson and Crick	$(i)$ Double helix model of $DNA$
$(2) \ 1928$	$(b)$ Friedrich Miescher	$(ii)$ Proof that $DNA$ is genetic material
$(3) \ 1869$	$(c)$ Griffith	$(iii)$ Nuclein
$(4) \ 1953$	$(d)$ Hershey and Chase	$(iv)$ Transforming principle

In which process does the transfer of genetic information occur from $RNA$ to $DNA$?

Which of the following contains the essential enzymes for protein synthesis?

How many of the following statements are correct?
$I - RNA$ is formed from $DNA$ by the process of transcription.
$II - DNA$ is more stable than $RNA$.
$III - RNA$ acts as a catalyst (enzyme) in some biochemical reactions.
$IV - DNA$ is resistant to mutations due to its double-helical structure and the presence of complementary strands that allow for repair mechanisms.

Distinguish between: $m-RNA$ and $t-RNA$.