Question

Which of the following pairs do not have the same number of classes in their crystal system?

• A. Cubic -- Tetragonal
• B. Monoclinic -- Orthorhombic
• C. Tetragonal -- Hexagonal
• D. Monoclinic -- Triclinic

Hint:

Cubic system has 5 crystal classes, while tetragonal system has 7 crystal classes.

Answer 1

The Correct Option is A

Concept:
Crystal systems contain different numbers of crystal classes. The number of classes depends on symmetry elements present in the system.

Step 1: Recall number of classes.
The cubic crystal system has: \[ 5 \text{ classes} \] The tetragonal crystal system has: \[ 7 \text{ classes} \]

Step 2: Compare the pair.
Since cubic has \(5\) classes and tetragonal has \(7\) classes, they do not have the same number of crystal classes. \[ 5\neq 7 \]

Step 3: Final conclusion.
Therefore, the pair that does not have the same number of classes is: \[ \text{Cubic -- Tetragonal} \] \[ \therefore \text{Correct Answer is (A)} \]