KNO₃

Molar mass = 101.1 g/mol
Potassium: (39.10 / 101.1) x 100 = 38.67%
Nitrogen: (14.01 / 101.1) x 100 = 13.86%
Oxygen: (48.00 / 101.1) x 100 = 47.48%

H₂SO₄

Molar mass = 98.07 g/mol
Hydrogen: (2.016 / 98.07) x 100 = 2.06%
Sulfur: (32.06 / 98.07) x 100 = 32.69%
Oxygen: (64.00 / 98.07) x 100 = 65.26%

C₂H₅OH

Molar mass = 46.07 g/mol
Carbon: (24.022 / 46.07) x 100 = 52.14%
Hydrogen: (6.048 / 46.07) x 100 = 13.13%
Oxygen: (16.00 / 46.07) x 100 = 34.73%

C₆H₅NH₂

Molar mass = 93.13 g/mol
Carbon: (72.066 / 93.13) x 100 = 77.38%
Hydrogen: (7.056 / 93.13) x 100 = 7.58%
Nitrogen: (14.01 / 93.13) x 100 = 15.04%