Arrange the following materials by increasing hardness (typical Mohs scale intuition): (a) Gold, (b) Iron, (c) Sand (quartz), (d) Diamond.

Introduction / Context:
Hardness is a material property reflecting resistance to scratching. The Mohs scale (qualitative) is often used in general knowledge contexts: higher values scratch lower ones. Gold is soft (around 2.5–3), iron is harder (around 4), common sand is largely quartz (around 7), and diamond is the hardest natural material (10). Hence you can rank them from softest to hardest.

Given Data / Assumptions:

• Approximate Mohs hardness: gold ~2.5–3, iron ~4, quartz (sand) ~7, diamond 10.
• We ignore alloys, treatments, and purity variations.

Concept / Approach:
Order by increasing hardness (softest → hardest). Compare approximate Mohs values and place each material accordingly. The monotonic increase must be preserved to avoid contradictions (e.g., a softer material cannot scratch a harder one).

Step-by-Step Solution:
Softest: Gold (a).Then: Iron (b).Then: Sand/quartz (c).Hardest: Diamond (d).Therefore: a, b, c, d.

Verification / Alternative check:
Check pairwise: diamond > quartz; quartz > iron; iron > gold. These pairwise truths enforce the overall order.

Why Other Options Are Wrong:

• d, c, b, a: Descending, not ascending.
• c, b, a, d: Puts quartz before iron then gold, which would be descending between b and a.
• a, b, d, c: Incorrectly places diamond before sand/quartz reversal.

Common Pitfalls:
Confusing “strength” or “value” with “hardness.” Hardness here is scratch resistance, not price or tensile strength.

Final Answer:
a, b, c, d