Explanation: To determine which frequencies are within legal tolerance, we must first calculate the allowable deviation for each nominal frequency based on the given 2 ppm (parts per million) accuracy. The question implies that the legal tolerance for these frequencies is 2 ppm, and the counter's accuracy adds to the uncertainty of measurement. Thus, we consider the overall tolerance as the sum of the legal tolerance and the counter's accuracy, which means a total of 4 ppm (2 ppm legal + 2 ppm counter accuracy) for practical measurement purposes. 1. **Calculate tolerance for 2182.0 kHz:** * Deviation = 2182.0 kHz * (4 / 1,000,000) = 2,182,000 Hz * 0.000004 = 8.728 Hz * Allowable range: 2182.0 kHz ± 0.008728 kHz (or 2181.991272 kHz to 2182.008728 kHz) 2. **Calculate tolerance for 4125.0 kHz:** * Deviation = 4125.0 kHz * (4 / 1,000,000) = 4,125,000 Hz * 0.000004 = 16.5 Hz * Allowable range: 4125.0 kHz ± 0.0165 kHz (or 4124.9835 kHz to 4125.0165 kHz) Now, let's evaluate each option: * **A) 2181.991 kHz and 4125.004 kHz** * For 2182.0 kHz: Deviation = |2182.000 - 2181.991| = 0.009 kHz = 9 Hz. This is greater than 8.728 Hz, so it's **out of tolerance**. * **B) 2182.006 kHz and 4124.995 kHz** * For 2182.0 kHz: Deviation = |2182.006 - 2182.000| = 0.006 kHz = 6 Hz. This is less than 8.728 Hz, so it's **within tolerance**. * For 4125.0 kHz: Deviation = |4125.000 - 4124.995| = 0.005 kHz = 5 Hz. This is less than 16.5 Hz, so it's **within tolerance**. * Since both frequencies are within their respective tolerances, this option is correct. * **C) 2182.010 kHz and 4124.992 kHz** * For 2182.0 kHz: Deviation = |2182.010 - 2182.000| = 0.010 kHz = 10 Hz. This is greater than 8.728 Hz, so it's **out of tolerance**. * **D) 2181.990 kHz and 4125.009 kHz** * For 2182.0 kHz: Deviation = |2182.000 - 2181.990| = 0.010 kHz = 10 Hz. This is greater than 8.728 Hz, so it's **out of tolerance**. Therefore, only option B has both measured frequencies within the calculated 4 ppm tolerance.