ambiguous which

[radhi]

When will we say the relative pronoun 'which' has ambiguous reference?

eg. cars come in many colours, which can be very cool or very ugly.
here it was said that 'Which' refers to both cars and colours.

But from OG i thought that 'which' refers only to noun before it (i.e here to colours only).
so could u plz clear my doubt?

similarly the rule for 'which' applies to 'whom' and 'whose' aslo?(i.e they also refers to noun before them?)

[esledge]

The "which can be very cool or very ugly" refers to "colors," the noun immediately preceding the comma. Your example is interesting, as the phrase could logically refer to the cars themselves, but only if the cars were immediately before the comma. The GMAT is very picky about the placement, and would therefore not consider your example ambiguous. I could imagine two grammatically correct sentences:

Cars are sold in many new colors, which can be very cool or very ugly.
Many new colors have been introduced for cars, which can be very cool or very ugly.

Same modifier, different modified noun, therefore different meaning regarding what is cool or ugly.

A small exception to the placement rule for "which," occurs when the noun you intend to modify with "which" also requires a short prepositional phrase as modifier to make sense. For example:

Many colors for cars, which can be very cool or very ugly, have been introduced over the years.

"Colors" is modified by both "for cars" (necessary to complete the meaning) and the "which" phrase. Some might argue that this is more ambiguous than your original example. For that reason, the GMAT tends not to test this exception.

Finally, yes, the rules for who/whose/whom are similar.