(d) : $DNA$ is a type of nucleic acid that forms genetic material in many organisms. It consists of a long polymer of nucleotides which transcribes the coded information in the form of a triplet code of nucleotides in $mRNA$. It is a double helical molecule. The two strands of $DNA$ run in opposite directions to one another with the hydrogen bonds between them. One strand of $DNA$ has $5'­3'$ direction and the other strand has $3'­5' $ direction. So they are antiparallel. This direction is determined by the presence of a free phosphate or $OH$ group at the end of the strand. If the strand has phosphate group at the the $5'$ end and with a free $OH$ group at the $3'$ end.