"The crystal system represented by a ≠ b ≠ c α=γ=90° β≠90° is called_________."

Monoclinic

The correct answer is 3. Monoclinic.

A monoclinic crystal system is a crystal system where the three axes are not all of equal length and the angles between the axes are not all 90 degrees. In a monoclinic crystal system, two of the axes are perpendicular to each other, but the third axis is not perpendicular to the other two axes. The angles between the axes are α=γ=90° and β≠90°.

The other crystal systems are:

• Orthorhombic:  The three axes are of equal length and the angles between the axes are 90 degrees.
• Tetragonal:  Two of the axes are of equal length and the angles between the axes are 90 degrees.
• Triclinic:  The three axes are not of equal length and the angles between the axes are not 90 degrees.