Right option is (b) α = β = 90o ϒ = 120o
Explanation: The crystal system is a system by which crystal structures are classified. Each crystal system is defined by the relationship between edge lengths a, b, and c and interaxial angles α, β, and ϒ. For hexagonal system, the interaxial angles are given by α = β = 90o ϒ = 120o.