In half wave rectification, if the input frequency is $60\text{Hz}$, then the output frequency would be:

In a half-wave rectifier, the output pulse occurs for every full cycle of the input wave. The time period of the output is the same as the time period of the input.Therefore, output frequency = input frequency = $60\text{Hz}$.(Note: For a full-wave rectifier, output frequency would be $2\times$ input frequency).