The correct answer is (a) Limestone.
Limestone is a sedimentary rock composed mainly of calcium carbonate (CaCO3). It is the most common sedimentary rock on Earth, and the most widely used industrial mineral. Limestone is used in the manufacture of cement, lime, and other building materials, as well as in the production of iron and steel, paper, and glass.
Dolomite is a sedimentary rock composed of calcium magnesium carbonate (CaMg(CO3)2). It is similar to limestone in appearance, but it is harder and denser. Dolomite is used in the manufacture of cement, lime, and other building materials, as well as in the production of magnesium metal and magnesium salts.
Soapstone is a metamorphic rock composed of talc (Mg3Si4O10(OH)2). It is a soft, white or gray rock that is easily carved. Soapstone is used for a variety of purposes, including making sculptures, countertops, and sinks.
Magnesite is a magnesium carbonate mineral (MgCO3). It is a white or gray mineral that is often found in veins or beds. Magnesite is used in the manufacture of magnesium metal, magnesium salts, and refractories.
The Bajun-Khurpatal area in the Lesser Himalaya is a major source of limestone. The limestone in this area is high quality and is used in the manufacture of cement, lime, and other building materials.