Which element is likely to have the highest thermal conductivity

sodium element is likely to have the highest thermal conductivity

1.cause they have wings

2.cause they are insects

3.cause they are

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.