A particle is moving eastwards with a velocity of ` 5 m//s`. In `10 s` the velocity changes to `5 m//s` nothwards. The average acceleration in this time is
A. Zero
B. `(1)/(sqrt(2)) m//s^2 N-W`
C. `(1)/(sqrt(2)) m//s^2 N- E`
D. `(1)/(sqrt(2)) m//s^2 S-W`