The correct option is (a) ρCμk^2/ε
Explanation: Using dimensional analysis, the turbulent dynamic viscosity can be given as
μt = Cμ ρϑl
Where,
ϑ → Velocity scale of large eddies
l → Length scale of large eddies
Substituting these two in k and ε terms, we get
μt = Cμ ρ\(\frac{k^2}{\varepsilon}\)
Where, Cμ is a dimensionless constant which is adjustable. The standard k-ε model uses Cμ=0.09.