Question

1. which crystal structure has the most workable metals?

1 point
○ simple cubic
○ bcc
○ fcc
○ hcp

1. which crystal structure has the most empty space?

1 point
○ simple cubic
○ bcc
○ fcc
○ hcp

1. what caused the bends in the iron wire to flatten down when the wire got hot?

1 point
○ fcc changing to bcc
○ bcc changing to fcc
○ bcc changing to hcp
○ fcc changing to hcp

Explanation:

Question 52

Workability of metals relates to their ability to deform. FCC (Face - Centered Cubic) structure has more slip systems (12) compared to BCC (Body - Centered Cubic, 48? No, BCC has 48? Wait, no: FCC has 12 slip systems, BCC has 48? No, correction: FCC has 12 slip systems, BCC has 48? No, actually, FCC has 12 slip systems, BCC has 48? Wait, no, the number of slip systems: FCC: {111}<110> (4 planes, 3 directions each, 43 = 12). BCC: {110}<111> (6 planes, 2 directions each, 62 = 12? No, I'm getting confused. Wait, the key point is that FCC metals are generally more workable. Metals with FCC structure (like Cu, Al, Au) are highly ductile. So among the options, FCC has the most workable metals.

The packing efficiency of different crystal structures: Simple cubic has a packing efficiency of about 52%, BCC is about 68%, FCC and HCP are about 74%. So the one with the most empty space is the one with the lowest packing efficiency, which is simple cubic.

Iron at room temperature (below 912°C) has a BCC (Body - Centered Cubic) structure (α - Fe). When heated above 912°C, it transforms to FCC (Face - Centered Cubic) (γ - Fe). This phase transformation (BCC to FCC) changes the atomic arrangement, and the FCC structure has a more close - packed arrangement, which can cause the iron wire to flatten as the structure changes and allows for easier deformation.

Answer:

C. FCC

Question 53