A molecular gas is classical if this quantity is much less than the cube root of inverse particle density. Entropy minus five-halves (20[1])is proportional to the negative logarithm of this quantity cubed times N over V in the Sackur–Tetrode equation. (20[1]0[2])This quantity was measured for electrons in an experiment to study Rutherford scattering off of nickel that inadvertently (0[1])produced a (*) Bragg pattern. This quantity (0[2])equals Planck’s constant (10[1])over linear momentum. (10[9]0[1])Diffraction (10[1])in Davisson–Germer (10[1])experiments (10[2])requires electrons or X-rays for which this quantity (0[1])approximates crystal (10[1])plane spacing. Duality gives particles a form (10[1])of this quantity named for Louis de Broglie. (10[5])For 10 points, name this quantity that varies inversely with frequency (10[1])for waves. (10[2]0[1])■END■ (10[6])