The correct answer is (d) Chert.
Chert is a hard, dense, fine-grained sedimentary rock composed of silica. It is typically white, gray, or brown in color, and can be translucent or opaque. Chert is often used to make stone tools, as it is a very durable material.
Quartzite is a hard, dense, metamorphic rock composed of quartz. It is typically white, gray, or pink in color, and can be translucent or opaque. Quartzite is often used to make stone tools, as it is a very durable material.
Basalt is a hard, dense, igneous rock composed of calcium, magnesium, iron, and silica. It is typically black or dark gray in color, and is often used to make building materials. Basalt is not typically used to make stone tools, as it is not as durable as other types of stone.
Flint is a hard, dense, sedimentary rock composed of silica. It is typically white, gray, or brown in color, and can be translucent or opaque. Flint is often used to make stone tools, as it is a very durable material. However, flint is not as common in Assam as chert.
Therefore, the correct answer is (d) Chert.