The standard curve was done at the wavelength of 362 nm for uniformity. We can use this function to determine the concentration at any absorbance value. At A = 0.782, c is,
A = (3.2 x 10^-1 M^-1)c
0.782 = (3.2 x 10^-1 M^-1)c
c = 2.44 M
The concentration of the triiodide solution is 2.44 M.