For a cubic unit cell, what is V_cell expressed as?

• A. a^2
• B. 4a^3
• C. 2a^3
• D. a^3

Answer: (D)

In a cubic unit cell, the edges form a cube with edge length a, so the cell’s volume is the product of the three edge lengths: a × a × a = a^3. The volume is a measure of space inside the cube, which scales with length cubed. The other expressions would correspond to area (a^2) or arbitrary multiples of the volume that don’t reflect the actual geometry of a single cube. For a conventional cubic unit cell, the volume is simply a^3.