Question

The crystal system characterized by three unequal axes which intersect at 90° is:

• A. Cubic
• B. Tetragonal
• C. Orthorhombic
• D. Monoclinic

Hint:

Orthorhombic = 3 unequal lengths, all 90° angles. Think of it as a stretched box in all directions, but with right angles preserved.

Answer 1

The Correct Option is C

Crystals are categorized into seven systems based on their unit cell dimensions and the angles between the edges.
Orthorhombic Crystal System:

• Defined by three mutually perpendicular axes that are all of unequal length.
• The axial relationship is: \[ a \neq b \neq c \quad \text{and} \quad \alpha = \beta = \gamma = 90^\circ \]
• Examples of materials with orthorhombic structure include sulfur, olivine, and aragonite.

Why the Other Options Are Incorrect:

• (A) Cubic: All three axes are equal in length and intersect at 90°. \[ a = b = c \]
• (B) Tetragonal: Two axes are equal, third is different, all angles are 90°. \[ a = b \neq c \]
• (D) Monoclinic: Axes are unequal, and only two angles are 90°, one is not. \[ a \neq b \neq c; \, \alpha = \gamma = 90^\circ, \, \beta \neq 90^\circ \]

Hence, the correct answer is Orthorhombic, which features three unequal sides and all 90° angles.