Anew computer has a model number, a part number, and a serial number. the model number is assigned by the manufacturer to identify the type of computer. the part number identifies one part of the smaller components that make up the computer. the serial number is unique to each computer produced and identifies it. which relation is a function?

(serial number, model number)

That's a function mapping each serial number to its model number.

 (part number, serial number)

That's not a function; the same part number is in computers with different serial numbers

 (model number, part number)

That one's a bit confusing.  Normally a given model would have more than one part number inside so this isn't a function.  But here the description says there's only one part number for each model, so that would be a function.

(model number, serial number)

Not a function, more than one serial number for a given model number.

                                                      hope it helps