In which of the following the electric dipoles are spontaneously polarised even in the absence of electric field.

Rochelle salt, also called Sodium Potassium Tartrate Tetrahydrate, a crystalline solid having a large piezoelectric effect (electric charge induced on its surfaces by mechanical deformation due to pressure, twisting, or bending), making it useful in sensitive acoustical and vibrational devices.

Therefore, the correct option is A