Consider the reaction below:

Question

Cgraphite(s) + F2(g) +1/2O2(g) → CF2O(g)
Which of the following is a correct rate expression?
1. rate = −2∆[O2]/∆t
2. rate = −∆[CF2O]/∆t
3. rate =∆[F2]/∆t
4. rate = −∆[Cgraphite]/∆t
5. rate =∆[Cgraphite]/∆t

Answer 1

4 and 5 can't be right because graphite is a solid.
3 isn't right because it must have a - sign.
2 isn't right because the sign is +.
That leaves 1 for the right answer.

The rate = 1/(1/2)dO2/dt which is 2dO2/dt.