Which elements has the largest atomic radius

If you mean out of these specific elements it would be Rb but if you mean out  of all the elements I do believe it to be Cs.

Explanation:

As you moved to the left and down the period table the atomic radius increases for each element.

a saline water is fed to a reverse osmosis unit at flow rate o rotameter connected to reject (retentate) line reads 8 installed in reject and permeate line reads 15.2 milli siemens/cm and 300 micro siemens/com respectively.