Thorium metal characteristics: which set of statements correctly describes thorium’s macroscopic appearance and mechanical behavior?

Introduction / Context:
Thorium is a silvery, actinide metal of interest for alternative nuclear fuel cycles. Recognizing its basic physical appearance and mechanical traits helps distinguish it from other structural and fuel materials in nuclear engineering contexts.

Given Data / Assumptions:

• We consider pure thorium metal under normal ambient conditions.
• Comparisons like “similar to silver” refer to hardness feel among common metals.
• Surface tarnish can occur, but intrinsic properties are the focus.

Concept / Approach:
Thorium is typically described as silvery and steel-like in luster when freshly cut. It is relatively soft (less hard than steels; closer to silver in hardness) and workable, demonstrating good ductility. These traits align with textbook descriptions and general metallurgy references, especially when unoxidized and properly handled.

Step-by-Step Solution:
Assess appearance: fresh thorium is bright, metallic, steel-like.Assess hardness: relatively soft, comparable to silver rather than hardened steels.Assess ductility: thorium can be drawn/formed, indicating notable ductility.Combine: all three statements hold—select “All (a), (b) and (c).”

Verification / Alternative check:
Standard materials descriptions categorize thorium as a soft, ductile, silvery metal that tarnishes in air—consistent with the selected combined statement.

Why Other Options Are Wrong:

• Any single statement alone is incomplete; the set of all three captures the common description.
• “Brittle and black” mischaracterizes fresh thorium; darkening is due to surface oxidation, not intrinsic brittleness.

Common Pitfalls:
Confusing surface oxidation color with bulk appearance; equating “actinide” with brittle behavior—thorium is comparatively ductile.

Final Answer:
All (a), (b) and (c).