What is another chemical name for thymine?

The correct answer is Option (2) → 5-methyl uracil

Thymine is a pyrimidine base found in DNA. Its structure is that of uracil with a methyl group at carbon 5, so its other chemical name is 5-methyl uracil. RNA has uracil in place of thymine. This is one of the two chemical differences between DNA and RNA; the other is the sugar (deoxyribose in DNA, ribose in RNA, which has an extra –OH group at the 2′ position).

NCERT Extract:
Structure of Polynucleotide Chain – “… In RNA, every nucleotide residue has an additional –OH group present at 2′-position in the ribose. Also, in RNA the uracil is found at the place of thymine (5-methyl uracil, another chemical name for thymine).”