a. Yes, it is possible for a line (y = mx + b) that passes through the origin (0, 0) to pass through no other rational points. An example of such a line is y = sqrt(2)x. This line passes through the origin (0,0), but the y-coordinate will only be a rational number if the x-coordinate is also a rational number and a perfect square.
b. Yes, it is possible for a line to pass through no rational points. An example of such a line is y = sqrt(2)x + sqrt(3). This line will never pass through any rational points because the y-coordinate will only be a rational number if both x and b are rational numbers and perfect squares, which is not possible in this case.