Question

The crystal system having dimensions $a \neq b \neq c$ and $\alpha = \beta = \gamma = 90^\circ$ is:

• A. Hexagonal
• B. Monoclinic
• C. Triclinic
• D. Orthorhombic

Hint:

When all angles are 90° but edge lengths are unequal, the crystal system is orthorhombic.

Answer 1

The Correct Option is D

Step 1: Recall the crystal systems.
- Cubic: $a = b = c$, $\alpha = \beta = \gamma = 90^\circ$.
- Tetragonal: $a = b \neq c$, $\alpha = \beta = \gamma = 90^\circ$.
- Orthorhombic: $a \neq b \neq c$, $\alpha = \beta = \gamma = 90^\circ$.
- Monoclinic: $a \neq b \neq c$, $\alpha = \gamma = 90^\circ \neq \beta$.
- Triclinic: $a \neq b \neq c$, $\alpha \neq \beta \neq \gamma \neq 90^\circ$.
- Hexagonal: $a = b \neq c$, $\alpha = \beta = 90^\circ$, $\gamma = 120^\circ$.

Step 2: Apply given condition.
The problem states: $a \neq b \neq c$ and $\alpha = \beta = \gamma = 90^\circ$.

Step 3: Match with system.
This is the definition of the orthorhombic system.

Final Answer: \[ \boxed{\text{(D) Orthorhombic}} \]