Let metal is M
when metal react with excess o2 is forms an oxide but we don't know the valency of metal
M. - M2Ox
mw - 25/100m + m
wt of o2 = 25/100m
M binds with O2
m - 25/100m
x. - 8gr(eq.w)
hence x= 8*m*100/ 25*m = 32gr

Introduction:
When a metal is burnt with an excess of oxygen (O2), it undergoes a chemical reaction known as combustion. During combustion, the metal reacts with oxygen to form a metal oxide. The increase in weight of the metal after combustion with excess oxygen is due to the addition of oxygen atoms from the surrounding air.

Explanation:
To determine the equivalent weight of the metal, we need to understand the concept of equivalent weight. The equivalent weight of a substance is the mass of the substance that combines with or displaces 1 mole of hydrogen ions (H+) or any other monovalent cation or reacts with 1 mole of electrons.

Step 1: Determining the weight gain:
Given that the metal's weight increases by 25% after combustion with excess oxygen, we can calculate the weight gain using the following formula:

Weight Gain = (25/100) * Initial Weight

Step 2: Calculating the equivalent weight:
To find the equivalent weight of the metal, we need to relate the weight gain to the number of moles of the metal.

Equivalent Weight = Weight Gain / Number of Moles

Step 3: Relating moles to weight:
To relate moles to weight, we need to use the concept of molar mass. The molar mass of a substance is the mass of one mole of that substance.

Molar Mass = Weight / Number of Moles

Step 4: Relating molar mass to equivalent weight:
The equivalent weight of a substance is equal to its molar mass divided by its valency.

Equivalent Weight = Molar Mass / Valency

Step 5: Putting it all together:
By substituting the values from the previous steps, we can calculate the equivalent weight of the metal as follows:

Equivalent Weight = (Weight Gain / Number of Moles) / (Molar Mass / Valency)

Conclusion:
By following the steps outlined above, you can determine the equivalent weight of the metal after it is burnt with an excess of oxygen. Remember to consider the weight gain, number of moles, molar mass, and valency of the metal in your calculations.