What is 3.5 mol coverted into mu moles?

mu moles = micro moles. "Micro" is a prefix in the metric system meaning "one millionth of a" as in "one millionth of a mole." This can also be written as (1/1000000) or most often 10^-6.

So, if you have 3.5 moles, you can simply multiply it by the conversion factor for moles to micro moles, which looks like this: 3.5 mol x (1 micro mol/10^-6 moles) = 3,500,000 micro moles.

An easier way is to move the decimal six digits to the right, as that's essentially what 10^-6 means.