The correct option is C particle (i) is speeding up while particle (ii) is speeding down.
The slope of displacement - time graph gives the instantaneous velocity. In figure (i), the slope is less in the beginning but it keeps on increasing with time. Thus, velocity of the particle increases with time and hence the particle (i) is speeding up.
In Figure (ii), the slope is more in the beginning and it keeps on decreasing with time. Thus, velocity of the particle decreases with time and hence the particle (ii) is speeding down.