'Iron' is correctly related to the state 'Solid'; in the same classification by states of matter, 'Mercury' should be related to which state?

Introduction / Context:
This analogy classifies substances by their common state under standard conditions. Iron is ordinarily a solid, so we must select the normal state of mercury at room temperature and pressure.

Given Data / Assumptions:

• Iron at room temperature is a solid metal.
• Mercury is a metallic element with unusual state behavior.
• We assume standard laboratory conditions (around 25°C, 1 atm).

Concept / Approach:
Maintain identical relation: substance → typical physical state at room temperature. The choice should reflect common scientific knowledge rather than extreme conditions.

Step-by-Step Solution:
1) Confirm first mapping: Iron → Solid (true at room temperature).2) Identify mercury's typical state at room temperature.3) Mercury is the only common metal that is liquid at room temperature.4) Therefore, Mercury → Liquid.

Verification / Alternative check:
Reference property tables list mercury's melting point around -38.83°C, well below room temperature, confirming its liquid state in ordinary conditions.

Why Other Options Are Wrong:

• Solid: Not true at room temperature for mercury.
• Gas/Vapour: Mercury vaporizes at much higher temperatures; not its standard state.
• None of these: Incorrect because 'Liquid' is correct.

Common Pitfalls:
Assuming all metals are solid at room temperature. Mercury is an important exception.

Final Answer:
Liquid