Final answer:
Lewis Carroll coined the term 'portmanteau' for a blended word like 'smog', which merges 'smoke' and 'fog'. The correct answer is (a) portmanteau.
Step-by-step explanation:
The 11-letter term that Lewis Carroll came up with for a blended word like smog, which is a combination of smoke and fog, is portmanteau. The answer to the question is option (a) a portmanteau. This term is used to describe a word that combines the sounds and meanings of two others, and Carroll famously used them in his works, such as Through the Looking Glass, where Humpty Dumpty explains how slithy means 'lithe and slimy' and mimsy is 'flimsy and miserable.'