Practice question

Given: A Si crystal with 5 × 10²⁸ atoms m^{-3 is doped with 0.5 ppm of pentavalent impurity. The number of donor electrons per cubic meter is: These values define the system as per NCERT data. Formula: 0.5 ppm = 0.5 × 10⁻⁶. This is the standard NCERT relation for this phenomenon. Substitution & Calculation: Number of donor atoms = 0.5 × 10⁻⁶ × 5 × 10²⁸= 2.5 × 10²² m^{-3, each contributing one electron. 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.