What is the Q code indicating that you want the other station to send slower?

The correct Q code to request that another station send their Morse code (CW) or text at a slower speed is "QRS." It is a polite and standard way to inform the sending station that their current speed is too fast for you to copy accurately. A very convenient memory aid for this code is to simply think of the letter "S" as standing for "Slower." The other options provided do not relate to transmission speed at all. "QRN" refers to atmospheric static, "QRM" refers to station interference, and "QRL" indicates that a frequency is busy.