Which of the following is a purine derivative?

The average energy of each hydrogen bond in $A-T$ pair is $x \, kcal \, mol^{-1}$ and that in $G-C$ pair is $y \, kcal \, mol^{-1}$. Assuming that no other interaction exists between the nucleotides,the approximate energy required in $kcal \, mol^{-1}$ to split the following double stranded $DNA$ into two single strands is:
$A$-$T$-$A$-$T$-$G$-$C$-$A$-$G$
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$T$-$A$-$T$-$A$-$C$-$G$-$T$-$C$

Which is a bicyclic base?

Which of the following is/are correct?

Given below are two statements:
Statement $I$: $A$ unit formed by the attachment of a base to $1'-$position of sugar is known as nucleoside.
Statement $II$: When nucleoside is linked to phosphorous acid at $5'-$position of sugar moiety,we get nucleotide.
In the light of the above statements,choose the correct answer from the options given below:

Out of the following isomeric forms of uracil,which one is present in $RNA$?