Answer : The rate constant for this reaction is,

Explanation :
To calculate the rate constant for zero order reaction, the expression used is:
![\ln [A]=-kt+\ln [A_o]](https://img.qammunity.org/2021/formulas/chemistry/college/6l40dplqu001moxruhc0fyzghv8i0an9sp.png)
where,
= initial concentration
= final concentration =
at 195 s
= final concentration =
at 385 s
k = rate constant = ?
Now put all the given values in the above expression, we get:
............(1)
and,
............(2)
Subtracting 1 from 2, we get:
![\ln (2.50* 10^(-2))-\ln (5.00* 10^(-2))=-k* 385+\ln [A_o]+k* 195-\ln [A_o]](https://img.qammunity.org/2021/formulas/chemistry/college/wnvzo0j16pxquo673alq622x97ubsffwcv.png)



Therefore, the rate constant for this reaction is,
