A single conversion receiver with a 9 MHz IF has a local oscillator operating at 16 MHz. The frequency it is tuned to is:

In a superheterodyne receiver, the mixer combines the incoming radio frequency (RF) and the local oscillator (LO) frequency to produce the intermediate frequency (IF). The relationship is defined by the mixing products: the IF is usually the difference between the LO and the RF (IF = |LO - RF|). Given a Local Oscillator operating at 16 MHz and an IF of 9 MHz, we can determine the tuned RF by calculating the difference or the sum. The possible RF frequencies would be 16 MHz - 9 MHz = 7 MHz, or 16 MHz + 9 MHz = 25 MHz. Since 25 MHz is not among the given options, the receiver must be tuned to 7 MHz. Distractors like 21 MHz are incorrect because they do not satisfy the mathematical relationship between the IF, LO, and RF.