Crystal structures — which metals are body-centred cubic (BCC) at room temperature? Select the correct group that primarily exhibits the BCC lattice among the listed options.

Introduction / Context:
Identifying the crystal structure of metals (BCC, FCC, HCP) is a foundational skill in materials engineering because structure influences slip systems, ductility, transformation behavior, and mechanical properties. This question tests recognition of BCC metals.

Given Data / Assumptions:

• Structure at or near room temperature unless otherwise specified.
• Pure elements (not alloys) under standard conditions.

Concept / Approach:
BCC metals include alpha-iron (ferrite) at room temperature, and refractory metals such as tungsten (W), chromium (Cr), and molybdenum (Mo). FCC metals include aluminium (Al), copper (Cu), nickel (Ni), silver (Ag), and lead (Pb). HCP metals include magnesium (Mg), zinc (Zn), titanium (Ti at room temperature is HCP), cobalt (Co is HCP at room temperature with a transition to FCC at higher temperature), and cadmium (Cd).

Step-by-Step Solution:
List BCC exemplars: alpha-Fe (below 910°C), W, Cr, Mo.Compare with options: only the group “alpha-iron, tungsten, chromium, molybdenum” matches BCC.Eliminate others: groups dominated by FCC or HCP metals cannot be BCC.

Verification / Alternative check:
Phase diagrams and materials handbooks confirm alpha-iron is BCC, while gamma-iron (austenite) is FCC at elevated temperatures. Refractory metals W, Cr, Mo are classic BCC metals with high melting points.

Why Other Options Are Wrong:

• Zn, Mg, Co, Cd, Sb, Bi: mainly HCP or rhombohedral (Sb, Bi), not BCC.
• Gamma-iron, Al, Cu, Pb, Ag, Ni: mostly FCC; gamma-iron is the FCC allotropic form of iron.
• “None of the above”: incorrect because a valid BCC set exists.

Common Pitfalls:
Mixing up gamma-iron (FCC) with alpha-iron (BCC) and overlooking cobalt’s temperature-dependent structure.

Final Answer:
alpha-iron, tungsten, chromium, molybdenum