Since the compound "KNO" is an unlikely solute, a possible reason you're getting the wrong answer is that you have the wrong formula for the compound. Assuming you did the calculation right using the "KNO" formula, if you use the formula for a real compound, potassium nitrite (KNO₂), you will get the correct answer. You can see this by comparing the ratio of the molar masses:
"KNO": 39.1 + 14 + 16 = 69.1 g/mol
KNO₂: 39.1 + 14 + 32 = 85.1 g/mol
(85.1/69.1) = (2.31 × 10⁵)/(1.88 × 10⁵)
In other words, check the formula.
EDIT: Even though my answer is correct as far as it goes, the units of "ppm" are not used by chemists much in expressing concentration. We think in molar concentrations. If the answer you want is mass "KNO" per mass of solution, the reason for your error is even simpler: you used 65 g for the mass of the solution instead of 80 g = 65 g + 15 g (65 g is just the mass of the solvent, not the solution.) Now that I've checked this possibility, that is probably what you're doing wrong:
(15 g)/(65 g) = 0.231 = 2.31 × 10⁵ ppm
(15 g)/(80 g) = 0.1875 = 1.88 × 10⁵ ppm
Nevertheless, KNO is a very unlikely solute.
