Answer
Consider the following calculations
Explanation:
first order reaction
k = (1/t)ln(a/x)
rate constant k = 0.0592 sec-1.
t = time = 0.865 min = 51.9 sec
a= initial concentration = 0.125 mol/L
x = after t sec concentration = ?
0.0592 = (1/51.9)ln(0.125/x)
x = 0.0058 mol/L