What device includes an adapter that decodes data sent in radio signals?

The device that includes an adapter that decodes data sent in radio signals is a modem. A modem (short for modulator-demodulator) is used to modulate digital data from a computer or network into analog signals for transmission over analog communication lines like telephone lines or radio signals. It also demodulates incoming analog signals back into digital data for reception by the computer or network. So, option A, "Modem," is the correct answer in this context.
No, it is not a router. A router is a device that connects two or more networks and forwards data packets between them. A router does not decode data sent in radio signals, but rather uses protocols such as TCP/IP to route the data to the correct destination. A modem, on the other hand, is a device that modulates and demodulates signals, converting digital data from a computer into analog signals that can be transmitted over telephone or cable lines, and vice versa1. A modem can also use radio waves to communicate with wireless devices, such as cell phones or laptops. Therefore, the correct answer to the question on the current web page context is option A: Modem.

as we know modem can work without router so how can modem work without decoding signals if router is correct option.

router does not convert or decode radio signals. modem does this work. router only responsible for conncetion between devices