Understanding the Problem:
We are given that a metal oxide MO contains 40% oxygen. We need to determine the equivalent weight of the metal.

Solution:
To solve this problem, we will use the concept of equivalent weight and the given percentage of oxygen.

Step 1: Determining the Molecular Formula
To find the equivalent weight of the metal, we first need to determine the molecular formula of the metal oxide.

Let's assume the metal as M and the oxygen as O. Since the metal oxide contains 40% oxygen, it means that 40% of the compound's mass comes from oxygen. This implies that the remaining 60% of the mass comes from the metal.

Step 2: Calculating the Mass of Oxygen
To proceed further, we need to consider the atomic masses of oxygen (O) and metal (M). The atomic mass of oxygen is approximately 16 g/mol.

Let's assume the molecular weight of the metal oxide MO as 'x' g/mol. Therefore, the mass of oxygen in MO will be 0.4x g/mol (40% of x).

Step 3: Calculating the Mass of the Metal
Since the remaining 60% of the mass comes from the metal, the mass of the metal in MO will be 0.6x g/mol.

Step 4: Determining the Equivalent Weight
The equivalent weight is defined as the weight of a substance that can react with or replace one mole of hydrogen ions (H+). It is given by the formula:

Equivalent weight = Molecular weight / n

Here, 'n' represents the number of hydrogen ions that can be replaced by one mole of the substance.

In this case, since we are dealing with a metal, 'n' will be equal to the valency of the metal (V).

Step 5: Final Calculation
To calculate the equivalent weight of the metal, we need to find the ratio of the mass of the metal to the number of moles of hydrogen ions it can replace.

Equivalent weight of metal (M) = Mass of metal (0.6x g/mol) / V

Summary:
In summary, to find the equivalent weight of a metal oxide MO containing 40% oxygen, follow these steps:
1. Determine the molecular formula of the metal oxide.
2. Calculate the mass of oxygen in the compound (0.4x g/mol).
3. Calculate the mass of the metal in the compound (0.6x g/mol).
4. Determine the valency of the metal (V).
5. Calculate the equivalent weight of the metal using the formula: Equivalent weight of metal (M) = Mass of metal (0.6x g/mol) / V.

12 gram