Explanation:

Definition of Urbane:
Urbane is an adjective that describes someone who is sophisticated, refined, and polite in social situations. It refers to a person who has a polished and courteous manner and is well-educated and cultured.

Explanation:
Out of the given options, the correct answer is option 'C', which is "Discourteous". This is because the word "urbane" is used to describe someone who is polite and well-mannered, while "discourteous" means lacking politeness or respect. The two words have opposite meanings, making option 'C' the correct choice.

Other Options:
Let's take a look at the other options and understand why they are incorrect:

a) Illiterate: This term refers to someone who is unable to read or write. It is unrelated to the meaning of "urbane", which is about social sophistication and politeness.

b) Backward: This term can have multiple meanings, but in the context of describing a person, it usually implies someone who is less advanced or progressive. It does not convey the idea of being sophisticated or refined, which is the essence of "urbane".

d) Orthodox: This term refers to conforming to traditional or established beliefs or practices, especially in religion. While it is possible for someone who is orthodox to be polite and well-mannered, it is not a direct synonym for "urbane". Being orthodox does not necessarily imply being cultured or sophisticated in social situations.

Conclusion:
In conclusion, the correct answer to the question is option 'C' because "discourteous" is the antonym of "urbane". The word "urbane" describes someone who is refined and polite, while "discourteous" refers to someone who lacks politeness or respect.