If you are referring to the letter "O", it only contains one, curved line that can technically go on forever. There is not more than one line, nor is there less than one line contained in this letter. If it had no lines, it wouldn't exist! This one line connects to itself in no particular part of this circular shape, but it lines up with itself to look as if there were no starting or stopping point. Maybe ask the person who made up words?
2
4
none.
Eight
None
6
just one
One pair.
a rhombus has 4 equal sides
only 1
O and X And H and I (Note "O" has many, actually an infinite number of, lines of symmetry)
An infinite number.