What is the value of the interplanar spacing d231 for the (2 3 1) plane of an FCC structure whose atomic radius is 0.125 nm?

Among the various materials related to electronics, the energy band gap is maximum in ________.

A cubic sample of edge length L is maintained at a temperature of 4 K. The speed of sound in the material of the sample is 5 × 103 m/s. The minimum value of L required to excite the lowest frequency phonon mode is closest to: