**Question:** White gold alloy predominantly is:

A. palladium
B. platinum
C. nickel
D. iridium

**Core Concept:**
White gold is an alloy that combines gold with one or more additional elements to achieve the desired color and hardness. These elements are usually palladium, platinum, nickel, and iridium.

**Why the Correct Answer is Right:**
White gold alloys are typically composed of gold, palladium, and sometimes platinum, nickel, and iridium. Palladium and platinum are responsible for the white appearance, while iridium is often added for hardness. Among the given options, option C (nickel) is typically avoided due to potential hypersensitivity reactions in some individuals, making it less suitable for creating white gold alloys.

**Why Each Wrong Option is Incorrect:**

A. Palladium: While palladium is a key component in white gold alloys, it is not the only one. Palladium alone would produce a yellowish color, not white.
B. Platinum: Platinum is another essential component in creating white gold alloys, but palladium is preferred due to its lower cost and comparable hardness.
C. Nickel: As mentioned earlier, nickel is often avoided due to potential hypersensitivity reactions, making it less suitable for creating white gold alloys.
D. Iridium: Iridium is added for hardness, but it is not the primary component responsible for the white appearance of white gold alloys.

**Clinical Pearl:**
When selecting a white gold alloy, it is essential to consider the combination of elements and their properties, such as appearance, hardness, and potential adverse reactions. Hypersensitivity to nickel can lead to adverse reactions in patients, making it critical to avoid or minimize nickel content in white gold alloys.

**Correct Answer:** C. Nickel

In a white gold alloy, nickel is typically avoided as it is not a primary component responsible for the alloy's white appearance and can cause adverse reactions in some individuals due to potential hypersensitivity.