Does a plane containing 2 points of a line contains the entire line?

Yes, a plane containing 2 points of a line contains the entire line. Let us consider two points on a plane and then draw a line segment joining those two points. Since the points lie on the plane so line segment has to lie completely on that plane too. Now if we extend the line segment indefinitely in both directions we get a line and that line also has to lie on the same plane since some definite part(line segment) of it(line) also lies on the same plane.