ppb, otherwise known as parts per billion, represents the number of parts either in grams or milliliters per one billion parts. And remember, one billion is 10 to the nine now, when in aqueous solutions, just remember that we can make the connection that one ppb equals one microgram per one leader. Now, when dealing with parts per billion in terms of mass, we're gonna say it's equal two g of solute divided by grams of solution times 10 to the nine. And when looking at parts per billion in terms of volume, it then becomes milliliters of solution divided by millimeters or millions of solute divided by milliliters of solution times 10 to the nine. So just keep in mind when dealing with parts per billion and a quick solution. There's this connection and also the difference between parts per billion when dealing with Mass and when dealing with volume