Critically examine the use of picaresque mode in any 18th century novel.
This question seems to call for you to select a work of literature that may be considered to be picaresque and then to examine in what ways it is picaresque and in what ways it isn't.
The earliest novels were called picaresque in that they involved a roguish main character who travelled widely, survived by means of their wits alone, and preyed on those less clever than themselves. These novels contrast the idea of chivalry with the idea of pursuing adventure for its own sake. They were also episodic, which meant that they were based around a series of single episodes which had no relation to the rest of the action in the book (kind of like when you miss an episode of Friends it doesn't really matter to the overall plot of the show). Lazarillo de Tormes and Don Quixote are examples of picaresque novels.
A very interesting work to pick for this would be Robinson Crusoe. You will want to compare how far this work fits in with the definition provided above. Based on this definition Robinson Crusoe doesn't really seem to have all the elements of a picaresque novel. It does focus on one man's experience, but we can hardly describe him as a rogue, and though he does survive by his wits and skill, he does not take advantage of Man Friday in any devious fashion. Also, it is not episodic - there is a clear plot that runs throughout the story. It therefore can be said to represent the development of the novel from picaresque into something more interesting, turning elements of the picaresque into one of the early examples of novels that we have today.