Correct Option: C

Flint glass is optical glass that has relatively high refractive index and low Abbe number (high dispersion). Flint glasses are arbitrarily defined as having an Abbe number of 50 to 55 or less. The currently known flint glasses have refractive indices ranging between 1.45 and 2.00. A concave lens of flint glass is commonly combined with a convex lens of crown glass to produce an achromatic doublet lens because of their compensating optical properties, which reduces chromatic aberration (colour defects). Flint glass also bear the property of heat resistant. Traditionally, flint glasses were lead glasses containing around 4–60% lead oxide; however, the manufacture and disposal of these glasses were sources of pollution. In many modern flint glasses, the lead can be replaced with other additives such as titanium dioxide and zirconium dioxide without significantly altering the optical properties of the glass. Electric Bulbs and Spectacle glasses are made of Flint glass.