CONFIG_CLOCK_50MHz is not available for thedefaultarchitecture x86.
Result is shown for architecture m68knommu
default or selected kernelversion does not have config value CONFIG_CLOCK_50MHz.
Result is shown for kernelversion 5.4.123

50MHz

configname: CONFIG_CLOCK_50MHz

CPU CLOCK Frequency
└─>50MHz
In linux kernel since version 2.6.12  
Select a 50MHz CPU clock frequency.