AP EAMCET Engineering 21 Sep 2020 Shift 2 Paper

(b) PPM or Parts Per Million is expressed as 1 milligram of substance per kilogram of parent substance.
Since, mass of toothpaste =500g=0.5kg,
and mass of fluoride ion =0.2g=200mg,0.5kg
toothpaste contains 200mg fluoride ions,
1kg toothpaste will contain 200×2=400mg fluoride ions.
Hence, concentration of fluoride ion is 400ppm or 4×102ppm.