A2.5% (by mass) solution concentration signifies that there is of solute in every 100 g of solution. 2. therefore, when 2.5% is expressed as a ratio of solute mass over solution mass, that mass ratio would be . 3. a solution mass of 1 kg is times greater than 100 g, thus one kilogram (1 kg) of a 2.5% ki solution would contain of ki.

Answer #1 is "there is 2.5 grams of solute in every 100 g of solution." 
We calculate for 2.5% by mass solution by dividing the mass of the solute by the mass of the solution and then multiply by 100.
Answer #2 is "that mass ratio would be 2.5/100 or 2.5 grams of solute/100 grams of solution." 
We weigh out 2.5 grams of solute and then add 97.5 grams of solvent to make a total of 100 gram solution, that is,
     mass of solute / mass of solution = 2.5g solute / (2.5g solute + 97.5g solvent)
                                                          = 2.5g solute / 100g solution
Answer#3 is "a solution mass of 1 kg is 10 times greater than 100 g, thus one kilogram (1 kg) of a 2.5% ki solution would contain 25 grams of ki."
We multiply 10 to each mass so that 100 grams becomes 1000grams since 1000 grams is equal to 1 kg:
     mass of solute / mass of solution = 2.5g*10/[(2.5g*10) + (97.5g*10)]
                                                          = 25g solute/(25g solute + 975g solvent)
                                                          = 25g solute/1000g solution
                                                          = 25g solute/1kg solution