Question:easy

Calculate the radius of atom of metal forming fcc unit cell having edge length \(360\) pm

Show Hint

For fcc, face diagonal equals 4r so r = a/(2 root 2).
Updated On: Oct 1, 2026
  • \(180.04\) pm
  • \(127.26\) pm
  • \(155.91\) pm
  • \(254.67\) pm
Show Solution

The Correct Option is B

Solution and Explanation

Step 1: Geometry:
On one face of the fcc cube, there is an atom at each corner and one in the centre. The diagonal of the face passes through three atoms touching each other: corner, centre, corner.

Step 2: Length along the diagonal:
That equals $r + 2r + r = 4r$. By Pythagoras, the face diagonal of a square of side $a$ is $a\sqrt{2}$.

Step 3: Solve:
$4r = 360 \times 1.4142 = 509.1$ pm, so $r = 509.1/4 = 127.3$ pm.

Step 4: Check with options:
Only $127.26$ pm matches within rounding.

Final Answer:
The atomic radius is 127.26 pm, option (B). \[ \boxed{127.26 \text{ pm}} \]
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