Identify the incorrect statements from the following.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → DNA has four bases Adenine, Cytosine, Guanine, Uracil
Nucleic acids are of two kinds, DNA and RNA. Each nucleotide has a pentose sugar, a phosphate and a nitrogenous base:
DNA: sugar β-D-2-deoxyribose; bases adenine (A), guanine (G), cytosine (C) and thymine (T); a double helix of two strands.
RNA: sugar β-D-ribose; bases adenine, guanine, cytosine and uracil (U); usually a single strand.
Uracil is found only in RNA; in DNA its place is taken by thymine.
Option (1) Pentose sugar in DNA is \(\beta \)-D-2-deoxyribose — A correct statement. “2-deoxy” means the –OH at C2 of ribose is replaced by H.
Option (2) DNA has four bases Adenine, Cytosine, Guanine, Uracil — The incorrect statement. DNA has thymine, not uracil; uracil is found only in RNA.
Option (3) Two strands of DNA are complementary to each other — A correct statement. The strands are held by hydrogen bonds between specific base pairs, adenine with thymine and cytosine with guanine, so the sequence of one strand fixes that of the other.
Option (4) DNA finger printing is used to identify racial groups to rewrite biological evolution — A correct statement. DNA fingerprinting is used in forensic work, to settle paternity, to identify dead bodies and to identify racial groups to rewrite biological evolution.
NCERT (2026-27 edition):
Chemical Composition of Nucleic Acids – …
