Question

For purpose of a practical energy producing reaction one wants a disintegration energy Q which is 

1. Positive for fusion and negative for fission
2. Negative for fusion and positive for fission
3. Negative for both fusion and fission
4. Positive for both fusion and fission

Answer 1

Correct Answer - Option 4 : Positive for both fusion and fission

CONCEPT:

• Radioactive decay is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive.
• Disintegration energy Q is the energy released during radioactive decay.

Nuclear Fission	Nuclear Fusion
Fission would be defined as the splitting of a large single atom into multiple atoms of small size.	Fusion would be defined as the joining of two or more small atoms to form a large atom.
Requires less energy to start.	A large amount of energy is required to start nuclear fusion.
The amount of energy released in fission is much lower than the energy released during fusion.	The amount of energy released in fusion is way higher than that of the fission reaction.
Normally it does not occur naturally.	It naturally takes place in stars and the Sun.
The fission reaction produces highly radioactive substances.	Very few radioactive chemicals come out of this reaction.
Uranium is one of the primary fuels.	Hydrogen isotopes are used as fuel.

EXPLANATION:

The disintegration energy Q is given as,

⇒ Q = (m_r - m_p) × 931 MeV     -----(1)

Where m_r = mass of reactant, and m_p = mass of the product (weights are in the units of atomic mass)

• If the value of disintegration energy Q is negative, that means the mass of the product is more than the reactant, which means the nuclear reaction rate is decreasing and after some time the nuclear reaction will stop.
• If the value of disintegration energy Q is positive, that means the mass of the product is less than the reactant, which means the nuclear reaction rate is increasing and the nuclear reaction will continuously happen.
• So for purpose of a practical energy-producing reaction one wants a disintegration energy Q positive for both fusion and fission.
• Hence, option 4 is correct.