The correct statement with regard to the secondary structure of DNA/RNA is:

The statement that is true about nucleic acids is: “DNA possesses a double‑strand helix structure and contains thymine as one of the four bases.”

**Why this is correct**
DNA (deoxyribonucleic acid) is composed of two complementary strands that wind around each other to form the familiar double‑helix. Each strand is made of nucleotides, and the four bases in DNA are adenine (A), guanine (G), cytosine (C), and thymine (T). Thymine pairs with adenine through two hydrogen bonds, stabilising the double‑helix.

**Why the other options are incorrect**
• Option 1 says DNA has a single‑strand helix and contains uracil. DNA is double‑stranded and uses thymine, not uracil.
• Option 2 claims RNA is single‑strand and contains thymine. RNA is indeed single‑stranded, but its fourth base is uracil, not thymine.
• Option 4 states RNA has a double‑strand helix and contains uracil. RNA is single‑stranded; while it does contain uracil, it does not form a double helix in its normal functional form.

Therefore, the only statement that accurately describes the structural and base composition characteristics of DNA is the one given as the correct answer.