Define spherical and chromatic aberrations for lenses?

Explanation:

1. Spherical Aberration: Most of the lenses are made from spherical surfaces as it is easy to make. When light rays passes through these lenses the rays which are closer to center refract less than the rays which are farther from the center. Because of this the quality of image is reduced as all the rays do not focus at a single point. This is known as Spherical aberration.

2. Chromatic Aberration: The refractive index of the lens varies with respect to the wavelength of the incident rays. The rays of different wavelength will deviate differently because of which all the colors will not focus at same point. This is known as chromatic aberration.

a charge 3q is at the origin, and a charge −2q is on the positive x axis at x=a. part a where on the x-axis would you place a third charge so it would experience no net electric force? enter an expression for the exact answer, which will involve a square-root sign. (do not enter an approximate decimal answer.)

i believe the answer is a