Question

Which of the following statements related to crystal defects is/are CORRECT?

• A. Screw dislocation is a type of planar defect
• B. Edge dislocation is a type of line defect
• C. Stacking fault is a type of line defect
• D. Cation vacancy is a type of point defect

Hint:

Sort each defect by how many dimensions it spans: a point, a line, or a plane, then match it to the claim.

Answer 1

The Correct Option is B, D

Step 1: Recall the classification of crystal defects.
Crystal defects are grouped by dimension. Point defects are zero dimensional, like a missing or extra atom. Line defects are one dimensional, like a dislocation. Planar defects are two dimensional, like a stacking fault or a grain boundary.

Step 2: Check option (A).
A screw dislocation is a line defect, because the distortion runs along a line through the crystal where atomic planes spiral around an axis. Calling it a planar defect is wrong.

Step 3: Check option (B).
An edge dislocation is caused by an extra half plane of atoms inserted into the lattice, and the boundary of that extra half plane is a line. So edge dislocation is correctly called a line defect.

Step 4: Check option (C).
A stacking fault is a break in the normal stacking sequence of atomic layers, for example an ABCABC sequence skipping a layer. This break happens over a plane, not a line, so stacking fault is a planar defect. Calling it a line defect is wrong.

Step 5: Check option (D).
A cation vacancy is a single missing positive ion in the lattice. Since it is a defect at one lattice site, it is a point defect. This statement is correct.

Step 6: Final conclusion.
The correct statements are edge dislocation as a line defect and cation vacancy as a point defect.
\[ \boxed{\text{(B) and (D) are correct}} \]