**Metal Carbonate Decomposition**

When a metal carbonate is heated, it undergoes a decomposition reaction, resulting in the formation of a metal oxide and the release of carbon dioxide gas. The general equation for this reaction can be represented as follows:

Metal Carbonate → Metal Oxide + Carbon Dioxide

For example, consider the decomposition of calcium carbonate (CaCO3):

CaCO3(s) → CaO(s) + CO2(g)

**Weight Loss during Decomposition**

During the decomposition of a metal carbonate, there is a loss in weight due to the release of carbon dioxide gas. This weight loss is attributed to the removal of the carbon and oxygen atoms present in the carbonate ion (CO3^2-).

In the given problem, it is mentioned that the metal carbonate is reduced to 60% of its original weight. This reduction in weight indicates that 40% of the original weight is lost during the decomposition reaction.

**Determining the Equivalent Weight**

The equivalent weight of a substance is defined as the weight of a substance that reacts with or is equivalent to one mole of hydrogen ions (H+). It is a measure of the reactivity or capacity of a substance to participate in a chemical reaction.

To determine the equivalent weight of the metal in the given problem, we need to consider that the metal carbonate is reduced to 60% of its original weight. This means that 40% of the original weight is lost due to the release of carbon dioxide gas.

Since the equivalent weight is based on the weight of a substance that reacts with one mole of hydrogen ions, we can assume that the original weight of the metal carbonate represents the weight of one mole of the metal carbonate.

Therefore, the equivalent weight of the metal can be calculated as:

Equivalent Weight = Original Weight / Loss in Weight

In this case, the loss in weight is 40% of the original weight, so the equivalent weight can be calculated as:

Equivalent Weight = Original Weight / (0.4 * Original Weight)

Simplifying the expression, we get:

Equivalent Weight = 1 / 0.4 = 2.5

Hence, the equivalent weight of the metal is 2.5.