Answer:(3)
Explanation: 2Al+3H2SO4----->Al(2SO4)3+3H2
Answer: It takes 3.120 seconds for the concentration of A to decrease from 0.860 M to 0.260 M.
Explanation:
Integrated rate law for second order kinetics is given by:
k = rate constant = 
= initial concentration = 0.860 M
a= concentration left after time t = 0.260 M

Thus it takes 3.120 seconds for the concentration of A to decrease from 0.860 M to 0.260 M.
1Hz = 1 cycle per second
19 cycles / .5 seconds = 38Hz
The answer is false. The correct answer would be efficiency.