# What is the concentration of a solution, in parts per million, if 0.02 gram of Na_3PO_4 is dissolved?

$1$ $\text{ppm}$ $=$ $1 \cdot m g \cdot {L}^{-} 1$. You have not given us a volume
A $\text{ppm}$ is so called because $1$ $L$ of water has a mass of $1$ $k g$, i.e. ${10}^{6}$ $m g$.
So if you have $0.020$ $g$, you have $20 \times {10}^{-} 3 \cdot g$, that is $20$ $m g$ or (!!IF THERE IS ONE LITRE OF SOLUTION!!) $20$ $\text{ppm}$.