Question

The two polynucleotide chains in DNA are
A. Parallel
B. Discontinuous
C. Antiparallel
D. Semi-conservative

Answer 1

In DNA, the opposite strands contain complementary bases. In a double-stranded DNA, one strand runs in the $5' \to 3'$ direction while the other runs in $3' \to 5'$i.e. the reverse direction.

Complete answer: DNA forms a double helix and nucleotides form the structural base of it. DNA has two strands with complementary nitrogen bases.
One of these strands runs in $3' \to 5'$direction while the other runs in the reverse direction $5' \to 3'$. They run in opposite directions but remain parallel.
In other words, the two polynucleotide chains are antiparallel to each other.
Their nitrogen bases project inward; these are joined by hydrogen bonds.

So, the correct option is C. Antiparallel

Note: DNA is a nucleic acid chain composed of deoxyribose sugar.
Francis Crick, J.D. Watson along with Rosaline Franklin had prepared a three-dimensional DNA model.
The antiparallel strands of DNA twist around a common axis to form the complete three-dimensional DNA structure- the double helix. It is known as the staircase model.