When three metals, 1, 2, and 3, are illuminated with light of frequency \(f\) in a photoelectric-effect experiment, the relationship of the stopping potential differences is found to be \(V_{\text {stop }, 1}>V_{\text {stop }, 2}>V_{\text {stop }, 3}\). Which material has

(a) the lowest frequency below which no electrons are ejected and

(b) the highest frequency below which the effect does not happen?