Question

What replaces thymine in RNA?
A. Guanine
B. Adenine
C. Uracil
D. Water

Answer 1

Hint: DNA has nitrogenous bases purines and pyrimidine’s purines are adenine (A) or Guanine (G) Pyrimidines are Thymine (T) and Cytosine (C).
RNA is a polymer of ribonucleotides each nucleotide unit is compared to a phosphate group, a $5 - $carbon ribose sugar and a nitrogen containing base. The bases in RNA are Adenine, Guanine, Uracil and Cytosine.

Complete answer:
A. Guanine – It is a base in DNA. In DNA molecules, guanine bases are located on one strand form chemical bonds with cytosine bases on the opposite strand.
 B. Adenine-It is one of the two purine nucleases used in forming nucleotides of the nucleic acids. In DNA, adenine binds to thymine via two hydrogen bonds. In RNA, Adenine binds to uracil.
In RNA, uracil replaces thymine.
Uracil binds to adenine via two hydrogen bonds.
In DNA, the uracil is replaced by thymine.
Uracil is a dimethylated form of thymine.
Each nucleotide in RNA contains a ribose sugar with carbons number $1'$and $5'$ and a bore is attached to the $1$ position.
D. Water- It is a transparent, odourless tasteless liquid.
It is composed of hydrogen and oxygen elements.
It occurs in solid, liquid and gaseous states.
Its characteristic feature is to dissolve many other substances in it.

Hence the correct answer is option (C) Uracil.

Note:The chemical nature of DNA was explained by PA Lerene. DNA is the largest macromolecule also, the largest macromolecule. A DNA molecule is a long double chain of deoxyribonucleotide unit, phosphate group, sugar and nitrogenous base.