Unit ppm stands for parts per million. in terms of mass, ppm is equivalent to mg/kg. since 1 kg is 10⁻⁶ mg, 1 kg is equivalent to million mg. therefore mg/kg is also ppm. there are 1.3 g of Ca ions in 3100 kg if 3100 kg contains - 1.3 g of Ca then 1 kg contains - 1.3 g / 3100 kg then Ca ions - 0.42 x 10⁻³ g/kg Ca ion concentration - 0.42 mg/kg therefore Ca ion concentration is 0.42 ppm
Paper is shredded, the paper is physically being shredded, iron rusting is due to oxygen reacting with it, gas is burned releases and odor which is a sign of chemical, shirt being bleached is chemical reaction.
