## **Core Concept**
The question tests knowledge of morphine toxicity, specifically the fatal dose in adults. Morphine is a potent opioid analgesic, and its overdose can lead to respiratory depression, which is often fatal. Understanding the toxicology of morphine is crucial for medical professionals.

## **Why the Correct Answer is Right**
The fatal dose of morphine in adults is generally considered to be around 200 mg. This dose can cause severe respiratory depression, leading to respiratory failure, which is usually the cause of death in morphine overdose cases. The exact dose can vary depending on factors such as the individual's tolerance, the presence of other central nervous system depressants, and the route of administration.

## **Why Each Wrong Option is Incorrect**
- **Option A:** 20 mg. This dose is much lower than the fatal dose and is actually within the therapeutic range for pain management. Therapeutic doses of morphine for analgesia typically range from 5 to 20 mg.
- **Option B:** 60 mg. While higher than the therapeutic dose, 60 mg is still below the generally accepted fatal dose of morphine.
- **Option D:** 400 mg. Although this is higher than the generally accepted fatal dose, it is not the best answer provided here given the options.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the fatal dose of morphine can vary and is highly dependent on individual factors. However, a commonly cited estimate for adults is around 200 mg. Naloxone is a specific antidote for opioid overdose, including morphine, and can be life-saving if administered promptly.

## **Correct Answer:** . 200 mg.