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PERCENTAGE (%)
Percent concentration implies so many units of solute per 100 units of solution.This can be either weight per volume (w/v), weight per weight (w/w), or volume per volume (v/v).
Examples
A 1% solution w/v contains 1 g of solute in 100 ml total volume of solution. For example the concentration of two aqueous solutions, one containing 1g of NaCl in 10 ml and the other 5 g of NaCl in 50 ml is 10% w/v.
A 1% solution w/w contains 1 g of solute in 100 g total weight of solution. (i.e. 1 g of solute plus 99 g of solvent).
A 1% v/v solution of ethanol in water would be 1 ml of ethanol plus 99 ml of water.
If the units are not specified, % is to be read as w/v i.e. g solute per 100 ml solution.