**Core Concept**
Wilson's disease is a rare genetic disorder characterized by excessive accumulation of copper in the body, particularly in the liver, brain, and other organs. This accumulation occurs due to mutations in the ATP7B gene, which is responsible for regulating copper transport and excretion.

**Why the Correct Answer is Right**
The correct answer is "Increased ceruloplasmin" because Wilson's disease is associated with low levels of ceruloplasmin, a copper-carrying protein in the blood. Normally, ceruloplasmin binds to copper and helps to transport it to the liver for excretion. In Wilson's disease, the mutated ATP7B gene leads to impaired copper transport, resulting in low ceruloplasmin levels and increased copper accumulation in the liver. This is a key diagnostic feature of the disease, and low ceruloplasmin levels are often used as a screening test.

**Why Each Wrong Option is Incorrect**
**Option A:** Increased copper content in liver is a feature of Wilson's disease, as the disease is characterized by excessive copper accumulation in the liver.
**Option C:** Mental changes are a common feature of Wilson's disease, particularly in the later stages of the disease, and can include symptoms such as tremors, rigidity, and difficulty with coordination and balance.
**Option D:** Features of chronic active hepatitis are also a common feature of Wilson's disease, as the excessive copper accumulation in the liver can lead to liver inflammation and damage.

**Clinical Pearl / High-Yield Fact**
Wilson's disease is often referred to as "hepatolenticular degeneration" due to its effects on the liver and the brain. This term is a useful mnemonic for remembering the disease's effects on these two critical organs.

**✓ Correct Answer: B. Increased ceruloplasmin**