What is the primary difference between two different isotopes?

Because different isotopes have different numbers of neutrons, they do not all weigh the same or have the same mass. Different isotopes of the same element have the same atomic number. They have the same number of protons. The atomic number is decided by the number of protons.

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Explanation:

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.