a) the number of particles on the positive X axis is equal to the number of paticles on the negative x-axis.

b) the total mass of the particles on the positive x-axis is the same as the total mass on negative x-axis.

c) the number of particles on the x-axis may be equal to the number of particles on the y axis.

d) If there is a particle on the positive X axis, there must be at least one particle on the negative x-axis.