Conservation Laws in Nuclear Reactions

Introduction:
In nuclear reactions, various quantities are conserved based on different fundamental laws. These laws ensure that certain properties remain unchanged before and after the reactions. Among these properties are mass-energy, momentum, and charge.

Conservation of Mass-Energy:
- According to the law of conservation of mass-energy, the total mass-energy of a closed system remains constant.
- In a nuclear reaction, the sum of the masses of the reactants is equal to the sum of the masses of the products.
- This means that the total mass before the reaction is equal to the total mass after the reaction.
- Although mass can be converted into energy and vice versa (as described by Einstein's mass-energy equivalence principle, E=mc^2), the total mass-energy is conserved.

Conservation of Momentum:
- According to the law of conservation of momentum, the total momentum of a closed system remains constant if there are no external forces acting on it.
- In a nuclear reaction, momentum is conserved before and after the reaction.
- Momentum is the product of mass and velocity, and since the masses and velocities of the reactants and products are different, the conservation of momentum is evident.
- The momentum of the reactants must be equal to the momentum of the products.

Conservation of Charge:
- According to the law of conservation of charge, the total charge of a closed system remains constant.
- In a nuclear reaction, the total charge before the reaction is equal to the total charge after the reaction.
- This means that the number of protons (which carry positive charge) and the number of electrons (which carry negative charge) must be conserved.

Conclusion:
In a nuclear reaction, the conservation of mass-energy, momentum, and charge are all observed. The total mass-energy of the system remains constant, the total momentum remains constant, and the total charge remains constant. Therefore, the correct answer is option 'D', which states that all of the above (mass-energy, momentum, and charge) are conserved in a nuclear reaction.