**Core Concept**
The question is testing knowledge of anaesthetic agents and their contraindications, specifically in patients with renal failure. The underlying principle is the pharmacokinetics and pharmacodynamics of anaesthetic agents and their impact on renal function.

**Why the Correct Answer is Right**
Lithium is a strong base that is primarily excreted by the kidneys. In renal failure, lithium can accumulate to toxic levels, leading to lithium toxicity. This is because the kidneys are unable to eliminate lithium effectively, resulting in its accumulation. Lithium toxicity can cause serious symptoms, including neurological effects, cardiac arrhythmias, and even death.

**Why Each Wrong Option is Incorrect**
**Option A:** Halothane is not contraindicated in renal failure. It is metabolized by the liver and does not have a significant impact on renal function.

**Option B:** Thiopentone is not contraindicated in renal failure. It is rapidly metabolized by the liver and does not accumulate to toxic levels in patients with renal impairment.

**Option C:** Succinylcholine is not contraindicated in renal failure. It is metabolized by plasma cholinesterase and does not have a significant impact on renal function.

**Clinical Pearl / High-Yield Fact**
In patients with renal failure, it is essential to choose anaesthetic agents that are primarily metabolized by the liver and do not accumulate to toxic levels in the body.

**Correct Answer:** D. Lithium.