To answer the question, calculate for the difference between the two values. That is, 22.1 g/cm³ - 21.2 g/cm³ which is equal to 0.9 g/cm³. Divide this value with the accepted value and multiply by 100%. This is shown below,
(0.9 g/cm³ / 22.1 g/cm³) x 100% = 4.07%
Thus, the percent error is approximately 4.07%.