Which square doesn't belong here and why?
3 (third square)
In all the other squares except
3rd square, 3 (three) lines divides the square in to 5 parts, while in 3rd square the lines (three lines) divides it to 6.
The big orange one. All the others are brown.
It's clearly the odd one out.
Only number 1...
has lines that meet the bounding square at a corner
Only number 2...
lacks any lines that slant down and to the right
Only number 3...
(a) divides the square into 6 areas instead of 5, (b) contains two complete intersections, and (c) includes a complete red triangle
Only number 4...
has no uniquely distinguishing characteristics. So my guess is 4.
1, 2 and 4
could be a part of representation of
number 4, mirrored or rotated.
But the picture in number
frame 3 because is the only one that shows the triangle created by the three lines through their pairwise intersections. In all four cases the (non-trivial) triangle exists, but in cases 1, 2 and 4 it is not presented within respective frame. (Edit: note that this is technically equivalent to AeJey's answer that observes the number of parts the frame is split into by the three lines.)
Clearly the odd one out is
1,3,2 are slices of a bigger picture. 4 does not fit with any of them. Even if we prolongue the lines in 1,2,3 they still fit well in the overall picture.
The answer is;
For three reasons:
When you extend the lines of 1, 2, and 4, they can join in a path of 3 lines which are in broken. You cannot do this with 3.
When you look at how many sections of white space there are in 1, 2, and 4 there's 5. In 3 there's 6
3 is the only square, where the lines within the frame make a triangle.
So obviously it has to be the answer stated above!