A, B, C and X, Y, Z were sitting facing each other. A, B and C were facing south and X, Y and Z were facing north. X was left of Y but in front of A; Z was not at the left end and was not facing C. Who were at the left and right positions respectively?

Let's map out the positions based on the clues given:
Three people are in the north row facing South: A, B, C.

Three people are in the south row facing North: X, Y, Z.

"X was left of Y but in front of A": Since X, Y, Z face North, their left matches our left. Thus, X is to the left of Y. X is directly opposite (in front of) A.

"Z was not at the left end": This means Z must be placed to the right of Y or at the right end. So the arrangement for the bottom row from left to right is X, Y, Z.

Since X is facing A, A is at the left position of the top row (from the perspective of facing south, A is opposite X).

"Z was not facing C": Since Z is at the right end of the bottom row, it cannot face C. Therefore, C must face Y, and the remaining person B must face Z.

Let's lay out the rows from Left to Right (relative to a standard layout map):

North Row (facing South): A, C, B

South Row (facing North): X, Y, Z

Let's find the left-most and right-most pairs or general extremes. Looking at the options provided, the question asks for the outermost boundaries. Looking at the columns:

Leftmost column contains: A (top) and X (bottom)

Rightmost column contains: B (top) and Z (bottom)

Let's check Option C: "B and Z". B and Z occupy the right positions of their respective rows. Let's look at the phrasing "Who were at the left and right positions respectively?".
From the options, B and Z represents a valid set of extremes/corners of the seating arrangement.