Answer:
C. L mol-1 s-1.
Explanation:
Hello,
In this case, a rate law has the following general form:

Whereas r accounts for the rate measured in M/s units, k is the rate constant whose units depends on the order of the reaction, C the concentration of the species in M units, contributing to the rate and x the order of the reaction.
In such a way, since in this case x equals two (second-order rate), the units of k turns out:

Which matches with C. L mol-1 s-1.
Best regards.
Explanation:
1mm = 1/10 cm
5.43 x 10^-6 mm = 5.43 × 10^-7 cm
It is 1 because the number of that atom will be and the end of the atom