Let's justify the $1^{st}$ statement
In winter:
The maximum concentration of pollutant = $8$ ppm
The minimum concentration of pollutant = $0$ ppm
Difference between the maximum and the minimum pollutant concentrations(in winter) = $8-0$ ppm = $8$ ppm
In Summer:
The maximum concentration of pollutant = $10.5$ ppm
The minimum concentration of pollutant = $1.5$ ppm
Difference between the maximum and the minimum pollutant concentrations(in summer) = $10.5-1.5$ ppm = $9$ ppm
∴ We can easily see that the difference between the maximum and the minimum pollutant concentrations are not same in both winter and summer.
So, statement i) is false.
Now, justify the justify the $2^{nd}$ statement
It says that- There are at least four days in the summer month such that the pollutant concentrations on those days are within 1 ppm of the pollutant concentrations on the corresponding days in the winter month.
So, we can see that statement ii) is true.
Hence, the correct option is $\textbf{B. only ii)}$.