Law of conservation of mass does not hold good when we talk of conversion of........into.......

Answer

**Step-by-Step Text Solution:**

1. **Understanding the Law of Conservation of Mass**: The law states that in a closed system, the total mass of reactants must equal the total mass of products in a chemical reaction. This means that mass cannot be created or destroyed.

2. **Identifying Exceptions**: While the law holds true for most chemical reactions, there are exceptions, particularly in nuclear reactions. In these reactions, the conversion of mass can occur.

3. **Nuclear Reactions**: In nuclear reactions, one element can be transformed into another element. This process involves changes at the atomic level, where the nucleus of an atom is altered.

4. **Example of Nuclear Reaction**: A classic example is the reaction involving Uranium-235, which can be bombarded with neutrons. This reaction produces Barium-141, Krypton nuclei, and additional neutrons, along with a significant release of energy.

5. **Mass Defect**: During nuclear reactions, there is a loss of mass known as the mass defect. This lost mass is not destroyed but is converted into energy, as described by Einstein's equation \(E=mc^2\).

6. **Conclusion**: Therefore, the law of conservation of mass does not hold good when we talk about the conversion of mass into energy, particularly in the context of nuclear reactions.

**Final Statement**: The law of conservation of mass does not hold good when we talk of conversion of mass into energy.

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