Given data:n=9.1×1028m−3σ=6.4×107S/mE=10N/Ce=1.6×10−19Cm=9.1×10−31kgStep 1. Relation between conductivity and relaxation time (Drude model)σ=mne2τ⇒τ=ne2mσStep 2. Substitute valuesτ=(9.1×1028)(1.6×10−19)2(9.1×10−31)(6.4×107)Compute step by step:Denominator:ne2=9.1×1028×(1.6×10−19)2=9.1×1028×2.56×10−38=2.33×10−9Numerator:mσ=9.1×10−31×6.4×107=5.82×10−23Now divide:τ=2.33×10−95.82×10−23=2.5×10−14sVAnswer:τ=2.5×10−14s