What is the chemical change in a $DNA$ molecule that leads to an alteration in the amino acid sequence during protein synthesis called?

What is the correct sequence of the complementary strand for the given portion of a DNA molecule:- $5' - G A C G T A C - 3'$?

Which of the following bases is a purine derivative?

Hydrogen bond is present in which two pairs of bases in the double helix structure of $DNA$?

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:

Identify the nucleoside from the following: