**Core Concept:** The atomic number of an element represents the number of protons in the nucleus of its atoms. Elements are arranged in the periodic table based on their increasing atomic number.

**Why the Correct Answer is Right:** The correct answer is **D**, which represents the atomic number of tungsten. Tungsten (W) is a chemical element with the symbol W and the atomic number 74. This means that each atom of tungsten has 74 protons in its nucleus, and it belongs to group 6 of the periodic table.

**Why Each Wrong Option is Incorrect:** Option **A** refers to the atomic number of sulfur (S), which is 16. Option **B** refers to the atomic number of phosphorus (P), which is 15. Option **C** is incorrect as it refers to the atomic number of gold (Au), which is 79.

**Clinical Pearl / High-Yield Fact:** Understanding the atomic numbers of elements is essential for medical students, as it helps in identifying elements in the periodic table and correlating them with their properties, chemical reactions, and biological roles. For instance, knowing that tungsten's atomic number is 74 allows you to identify it quickly in the periodic table and understand its unique properties, such as its high melting point and hardness, which makes it useful in various industrial and medical applications.

**Correct Answer:** .