For a real time clock, typically the oscillator's frequency is $32\mathrm{.}768kHz$ because:$-$

Select one:

a$.$ clock based counters wont work at other frequencies

b$.$ oscillator is unstable at other frequencies

C$.$ oscillators cannot be produced below $32\mathrm{.}768kHz$

d$.$ the oscillator at $32\mathrm{.}768kHz$ can be produced in any technology node from $250nm$ to $28nm$

e$.$ frequency is exactly $2^{15}$ cycles per second