If λ0 stands for mid-wavelength in the visible region, the de Broglie wavelength for 100 V electrons is nearest to

Order of magnitude calculation is enough.λ=hp=h2meeV1/2=6.6×10−34Js2×9×10−31×100×1.6×10−191/2≈10−10m  Mid-wavelength in visible region isλ0≈5000×10−10m Thus, λ=λ0/5000