Practice question

Given: A pure Si crystal is doped with 1 ppm of pentavalent impurity. If the Si atom density is 5 × 10²⁸ m^{-3, the number of donor atoms per cubic meter is: These values define the system as per NCERT data. Formula: 1 ppm = 1 part per million = 10⁻⁶. This is the standard NCERT relation for this phenomenon. Substitution & Calculation: Number of donor atoms = 10⁻⁶ × 5 × 10²⁸= 5 × 10²² m^{-3 . These contribute electrons, assuming full ionization at room temperature. Result: The computed value matches the expected outcome and confirms the correct choice. Units and powers like J kg⁻¹ K⁻¹, m/s², 10⁻⁵ are properly used as per NCERT.