Which of the following correctly fills in the missing information for the human X chromosome, given that it is a sex chromosome? (Assume the chromosome is not associated with a specific nuclide, but consider the number of DNA molecules, protons, and neutrons in a typical nucleotide of the X chromosome.)

• A. 1 DNA molecule, 17 protons, 17 neutrons per nucleotide
• B. 1 DNA molecule, 15 protons, 15 neutrons per nucleotide
• C. 1 DNA molecule, 10 protons, 10 neutrons per nucleotide
• D. 2 DNA molecules, 17 protons, 17 neutrons per nucleotide

Answer: (A)

Verified step by step guidance

1. Step 1: Understand that a human chromosome, including the X chromosome, consists of a single continuous DNA molecule. Therefore, the number of DNA molecules per chromosome is typically 1.
2. Step 2: Recall that DNA is made up of nucleotides, each containing a nitrogenous base, a sugar, and a phosphate group. The question asks about the number of protons and neutrons per nucleotide, so focus on the atomic composition of the nucleotide components.
3. Step 3: Identify the typical elements in a nucleotide: carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and phosphorus (P). Each element has a characteristic number of protons (atomic number) and neutrons (which can vary but are often close to the number of protons for common isotopes).
4. Step 4: Consider the nitrogenous bases (adenine, thymine, cytosine, guanine) and the phosphate group, which contains phosphorus. Phosphorus has 15 protons and typically 16 neutrons, nitrogen has 7 protons and about 7 neutrons, and oxygen has 8 protons and 8 neutrons. The total protons and neutrons per nucleotide will be a sum of these atomic numbers.
5. Step 5: Use this atomic information to match the given options, focusing on the correct number of DNA molecules (1) and the approximate number of protons and neutrons per nucleotide (commonly around 17 for both, considering the phosphate and nitrogenous base composition).