The balanced equation of the reaction is:
O3(g) + NO (g) → O2 (g) + NO2 (g)
Then the ratios of reaction is 1 mol O3 : 1 mol NO : 1 mol O2 : 1 mol NO2
If you have initially 0.05 M of O3 and 0.02 M of NO, the reaction will end when all the NO is consumed.
The by the stoichiometry 0.02 mol of O3 will be consumed in 8 seconds.
And the rate of reaction is change in concetration divided by the time.
The change in concentration in O3 is 0.02 M
Then, the rate respect O3 is 0.02 M / 8 seconds = 0.0025 M/s
The correct option is this: SODIUM IS VERY REACTIVE BECAUSE IT DOES NOT HAVE A FULL VALENCE SHELL.
For an atom to attain an octet form, it must have eight electrons in its outermost shell. Elements with eight electrons in their outermost shells are un-reactive. Sodium has only one electron in its outermost shell, this makes it to be very reactive because it is very willing to react with suitable elements in order to become stable.