Final answer:
In a superheterodyne receiver, the RF amplifier is responsible for determining the image rejection ratio by amplifying the desired signal and attenuating the image frequency.
Step-by-step explanation:
The part of a superheterodyne receiver that determines the image rejection ratio is the RF amplifier. The image frequency is an unwanted frequency that is capable of passing through the RF stage and reaching the mixer where it will produce an undesired signal at the intermediate frequency (IF). The ability of the receiver to reject this unwanted signal is referred to as the image rejection ratio. A higher ratio implies better rejection of the image frequency. The RF amplifier contributes to the image rejection by amplifying the desired signal and attenuating signals at the image frequency.