The correct answer is: a) Bell metal.
Bell metal is an alloy of copper and tin, with a small amount of zinc. It is a very hard and durable metal, and it is often used to make bells, gongs, and other musical instruments. It is also used to make decorative objects, such as xorai.
Iron is a metal that is found in nature. It is a very strong metal, and it is often used to make tools and weapons. However, it is not as durable as bell metal, and it is more likely to rust.
Silver is a metal that is found in nature. It is a very soft metal, and it is often used to make jewelry. It is also used to make coins and other decorative objects. However, it is not as durable as bell metal, and it is more likely to tarnish.
Gold is a metal that is found in nature. It is a very soft metal, and it is often used to make jewelry. It is also used to make coins and other decorative objects. However, it is not as durable as bell metal, and it is more likely to tarnish.
Xorai is a traditional Assamese object used for offerings. It is a bell-shaped object that is made from bell metal. It is often decorated with intricate designs, and it is used in religious ceremonies.