JEE Main · 2019 · 10 Jan 2019 · Shift 1 · Solid State

Which primitive unit cell has unequal edge length

(a \neq = b \neq = c)

and all axial angles different from

9 0^{\circ}

Answer: (A)

Solution

The crystal system that demands all three edge lengths be different and all three axial angles be unequal and none equal to

9 0^{\circ}

is the triclinic system, the least symmetric of the seven. Every other system keeps at least one angle at

9 0^{\circ}

or some edges equal, so only the triclinic cell meets both conditions at once.

JEE Main · 2019 · 10 Jan 2019 · Shift 1 · Single correct option