In the following question, out of the four alternatives, choose the one which can be substituted as a single word for the description: "A remedy for all diseases."

Introduction / Context:
This vocabulary question asks for a one-word substitute that means "a remedy for all diseases". Such questions are very common in English sections of competitive exams because they test both your vocabulary and your ability to distinguish between similar sounding words. The word you are looking for here has roots in ancient mythology and medical beliefs.

Given Data / Assumptions:

• Description: a remedy for all diseases.
• That implies a cure that can solve every illness, not just one or two.
• Options feature words associated with medicine or magic: Tonic, Nectar, Panacea, Elixir, Placebo.
• We assume exam standard dictionary meanings, not casual usage.

Concept / Approach:
The correct one-word substitute for a universal cure is "panacea". Historically, panacea referred to a mythical medicine able to cure every disease. In modern English, it also has a figurative meaning of a solution that is supposed to fix every problem. A tonic is a strengthening medicine, an elixir is a magical or medicinal potion, nectar is the drink of the gods, and a placebo is a dummy medicine with no real active drug. Only "panacea" specifically captures the idea of a remedy for all diseases.

Step-by-Step Solution:
Step 1: Focus on the extreme phrase "for all diseases", which indicates something universal.Step 2: Recall the term from general vocabulary: panacea, often used in phrases like "There is no panacea for all social problems."Step 3: Compare this meaning with the list of options provided.Step 4: Confirm that "panacea" is present and fits the description exactly.Step 5: Eliminate other words that mean a drink, a simple medicine, or a fake cure.

Verification / Alternative check:
Use the word in a sentence: "Some people think that one pill can be a panacea for every health problem, but doctors strongly disagree." This sentence reflects the idea of a cure for all illnesses. Try substituting "tonic" or "elixir" and the sentence loses the sense of universality. A tonic may improve health in general but is not claimed to cure every disease. An elixir is more of a magical or legendary potion. Hence, only panacea matches the meaning required by the question.

Why Other Options Are Wrong:

• Tonic: A tonic is a medicine that gives strength or energy but is not a cure for all diseases.
• Nectar: In mythology, nectar is the drink of the gods, and in botany it is a sweet liquid in flowers. It does not literally mean an all purpose cure.
• Elixir: An elixir can be a magical or medicinal drink, but the word alone does not guarantee that it cures every possible disease.
• Placebo: A placebo is a harmless pill or medicine with no therapeutic effect, often used in clinical trials as a control.

Common Pitfalls:
Because words like "elixir" and "nectar" sound poetic and powerful, many students pick them without recalling the specific meaning of "panacea". Remember that exam writers love to include attractive but incorrect choices. When the description uses absolute phrases like "for all diseases" or "cure for everything", panacea is the standard vocabulary answer.

Final Answer:
The correct one-word substitute for "a remedy for all diseases" is Panacea.