yes
Yes and they are the end points
line or a segment
No. A ray is infinite on one side and ends at a point at the other. A line segment ends in two points. A ray can contain a line segment, as the distance between any two given points on the ray is a line segment.
If 2 points determine a line, then a line contains infinitely many planes.
No, a circle can never pass through three points of a straight line. The circle will touch 1) no points of the line, 2) one point of the line (which is now tangent to the circle), or 3) two points of the line. A line can contain (at most) twopoints that lie on the line.
No. Two points determine one line, and only one.
YES. The intersection of two planes always makes a line. A line is at least two points.
It contains the whole line.
If you have two points, a and b, you can draw only one line that will go through both points. Or in other words, two points define a line.
In plane geometry a line is a two dimentional object between two points. If a line or a point is not on the line it, by definition, does not contain them. The answer therefor is infinite. Unless it is a closed line which has a slightly different definition but the answer is the same.
Any three points will determine a plane, provided they are not collinear. If you pick any two points, you can draw a line to connect them. An infinite number of planes can be drawn that include the line. But if you pick a third point that does not lie on the line. There will be exactly one plane that will contain the line and that point you added last. Only oneplane can contain the line, which was determined by the first two points, and the last point.
There is only one line (or line segment) that can be drawn between two distince points.