Unlike gradualism, punctuated equilibrium involves
a. a slow change in evolution over time.
b. stable periods of change interrupted by rapidly occurring change.
c. species that are said to be in equilibrium.
d. a steady change in evolution over time.

Punctuated equilibrium has been a theory in evolutionary biology developed and coined by Stephen Jay Gould which talks about very rapid changes which occur in nature while on the other hand still having a lot of stable periods with plenty of change in general. 

The correct answer for that reason would be  B.