meters per second squared is the appropriate units for acceleration units.
So the dimensions of acceleration is
Any answer that comes under that definition is correct.
Km/h² or m/s/s are the appropriate units of the acceleration.
Acceleration is the rate change of velocity of an object. it is given by
Δv= change in speed
Δt= time taken
Δv is measured in meter of km
Time is measured in second s or hour h
so the units of acceleration are km/h² or m/s/s
are perfectly good units of acceleration.
The only one that isn't is the one in the middle: ft/s