Question

A 2.5% (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

Answer #1. A 2.5% (by mass) solution concentration signifies that there is 2.5 grams of solute in every 100 g of solution. 
To calculate 2.5% by mass solution, we divide the mass of the solute by the mass of the solution and then multiply by 100.

Answer #2. therefore, when 2.5% is expressed as a ratio of solute mass over solution mass, that mass ratio would be 2.5/100 or 2.5 grams of solute/100 grams of solution. 
This means that weighing out 2.5 grams of solute and then adding 97.5 grams of solvent would make a total of 100 gram solution:
     mass of solute / mass of solution = 2.5g solute / (2.5g solute + 97.5g solvent)
                                                          = 2.5g solute / 100g solution

Answer#3. a solution mass of 1 kg is 10 times greater than 100 g, thus 1kg of a 2.5% ki solution would contain 25 grams of ki.
Since 1000 grams is 1 kg, we multiply 10 to each mass so that 100 grams becomes 
1000grams:
     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