Refractory materials — choose the correct sequence in order of increasing melting point (lowest to highest).

Introduction / Context:
Refractory selection hinges on resistance to softening and melting at high temperatures, slag interactions, and thermal shock. Knowing the relative melting (or softening) ranges of common refractories helps in lining furnaces, kilns, and converters. This question tests your ability to order four typical refractories by increasing melting point (from the lowest to the highest).

Given Data / Assumptions:

• Candidates: bauxite-based (alumina-silicate), chromite-based, dolomite (CaO·MgO), and magnesia (MgO).
• We consider general refractoriness/softening ranges commonly cited for these families.
• Compositional variations exist; the ordering reflects standard practice ranges.

Concept / Approach:
Alumino-silicate refractories (bauxite) typically have lower softening points than basic refractories. Chromite refractories offer good slag resistance but similar or slightly higher refractoriness than many bauxitic bricks. Dolomite and especially magnesia exhibit higher melting/softening points due to basic oxides with very high thermal stability. Thus the ascending order is usually alumino-silicate < chromite < dolomite < magnesia.

Step-by-Step Solution:

Verification / Alternative check:
Handbooks on refractories frequently present magnesia as a top performer for melting point, followed by other basic refractories like dolomite, while alumino-silicates sit lower in the hierarchy; chromite commonly lies between bauxite and dolomite for refractoriness.

Why Other Options Are Wrong:

• Dolomite, Magnesia, Bauxite, Chromite: Starts with a basic refractory, contradicting known hierarchy.
• Magnesia, Bauxite, Dolomite, Chromite: Places magnesia (highest) at the lowest position.
• —: Not a valid sequence.

Common Pitfalls:
Overlooking compositional variability; despite ranges, the general order used in practice matches option B.

Final Answer:
Bauxite, Chromite, Dolomite, Magnesia