Answer:
The types of slope for each pair are:
(2, 4) and (5, 1) => Negative
(3,5) and (-1,2) => Positive
(-7, 8) and (-7,0) => Undefined
(6.-3) and (4, -3) => Zero
Explanation:
We will find the slope of each line to check the type of slope.
Slope is given by the formula:

Here (x1,y1) are the coordinates of first point and (x2,y2) are coordinates of second point
Now,
(2, 4) and (5, 1)

The slope is negative.
(3,5) and (-1,2)

The slope is positive
(-7, 8) and (-7,0)

division by zero makes the slope undefined.
(6.-3) and (4, -3)

The slope is zero
Hence,
The types of slope for each pair are:
(2, 4) and (5, 1) => Negative
(3,5) and (-1,2) => Positive
(-7, 8) and (-7,0) => Undefined
(6.-3) and (4, -3) => Zero