Answer: 0.0115 M/s
Justification:
1) Assuming constatn volume, the rate or velocity of reaction is:
rate = change in concentration / time
2) The change is concentration is 0.100 M - 0.655 M = 0.345 M
3) The time was 30 s
4) Therefore the rate is: 0.345 / 30s = 0.0115 M/s