Question:hard

A metal has a fcc structure if the edge length of unit cell is 200 pm, calculate the volume occupied by particles in a unit cell.

Show Hint

Use r = a root 2 over 4 for fcc, then multiply the volume of one sphere by 4 atoms per cell.
Updated On: Oct 1, 2026
  • \(2.08\times 10^{-24} \text{cm}^3\)
  • \(5.92\times 10^{-24} \text{cm}^3\)
  • \(8\times 10^{-24} \text{cm}^3\)
  • \(3.14\times 10^{-24} \text{cm}^3\)
Show Solution

The Correct Option is B

Solution and Explanation

Step 1: Approach
Use the packing efficiency of fcc, which is 74 percent, applied to the volume of the unit cell.

Step 2: Volume of the unit cell
\[ a=200\ \text{pm}=2\times10^{-8}\ \text{cm},\qquad a^3=8\times10^{-24}\ \text{cm}^3 \]

Step 3: Volume occupied
Packing fraction for fcc is $\dfrac{\pi}{3\sqrt2}=0.7405$.
\[ V_{occ}=0.7405\times8\times10^{-24}=5.92\times10^{-24}\ \text{cm}^3 \]

Step 4: Conclusion
Option (C), $8\times10^{-24}$ cm$^3$, is the whole cell, not only the atoms. The atoms alone occupy $5.92\times10^{-24}$ cm$^3$, so the answer is (B).

Final Answer:
The four atoms in the fcc cell fill $5.92\times10^{-24}\ \text{cm}^3$, option (B). \[ \boxed{5.92\times10^{-24}\ \text{cm}^3} \]
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