The correct answer is (a) Gold.
Gold is a precious metal that is found in very small quantities in Gujarat. It is not a major mineral resource in the state.
Lignite is a type of coal that is found in significant quantities in Gujarat. It is used to generate electricity and produce steel.
Bentonite is a type of clay that is found in significant quantities in Gujarat. It is used in a variety of industrial applications, including drilling mud, cosmetics, and pharmaceuticals.
Limestone is a type of rock that is found in significant quantities in Gujarat. It is used in a variety of construction applications, including concrete, cement, and road construction.