History of spherical mirrors in human civilization

Parabolic mirrors were described and studied in classical antiquity by the mathematician Diocles in his work On Burning Mirrors. conducted a number of experiments with curved polished iron mirrors, and discussed plane, convex spherical, and concave spherical mirrors in his Optics. Parabolic mirrors were also described by the physicist Ian Sal in the 10th century, and Ian AL-Haythamdiscussed concave and convex mirrors in both cylindrical and spherical geometries, carried out a number of experiments with mirrors, and solved the problem of finding the point on a convex mirror at which a ray coming from one point is reflected to another point. By the 11th century, clear glass mirrors were being produced in Moorish Spain.

The answer is b.the gaseous state is electrically positive, while the plasma state is electrically negative.