To calculate the percentage composition of KNO3, we need to determine the mass of each element present in the compound relative to its total mass. Here's how we can calculate it:

1. First, find the molar mass of KNO3:

- Molar mass of K = 39.098 g/mol

- Molar mass of N = 14.007 g/mol

- Molar mass of O = 15.999 g/mol

- Molar mass of KNO3 = (1 × 39.098 g/mol) + (1 × 14.007 g/mol) + (3 × 15.999 g/mol) = 101.103 g/mol

2. Next, calculate the mass of each element in 1 mole of KNO3:

- Mass of K in 1 mole of KNO3 = 1 × 39.098 g = 39.098 g

- Mass of N in 1 mole of KNO3 = 1 × 14.007 g = 14.007 g

- Mass of O in 1 mole of KNO3 = 3 × 15.999 g = 47.997 g

3. Finally, calculate the percentage composition of each element:

- % K = (Mass of K / Molar mass of KNO3) × 100%

= (39.098 g / 101.103 g/mol) × 100%

= 38.67%

- % N = (Mass of N / Molar mass of KNO3) × 100%

= (14.007 g / 101.103 g/mol) × 100%

= 13.85%

- % O = (Mass of O / Molar mass of KNO3) × 100%

= (47.997 g / 101.103 g/mol) × 100%

= 47.48%

Therefore, the percentage composition of KNO3 is approximately 38.67% K, 13.85% N, and 47.48% O.