(a) Difference between Nuclear Fission and Fusion

Feature	Nuclear Fission	Nuclear Fusion
Definition	A heavy nucleus splits into two lighter nuclei.	Two light nuclei combine to form a heavier nucleus.
Condition	Occurs at room temperature (usually induced by neutrons).	Requires extremely high temperature and pressure.
Energy	Energy released per nucleon is relatively lower.	Energy released per nucleon is significantly higher.

[1 Mark for any two valid points of difference]

(b) Calculation of Energy Released

Step 1 (Formula & Given Data): [0.5 Mark]

The total energy released ($E_{total}$) is given by:

$$E_{total} = N \times E_{fission}$$

Where:

• $N$ = Number of atoms in 1 g of ${}_{94}\text{Pu}^{239}$
• $E_{fission} = 180 \text{ MeV}$
• Avogadro's number ($N_A$) = $6.023 \times 10^{23} \text{ atoms/mol}$
• Molar mass ($M$) = $239 \text{ g/mol}$

Step 2 (Step-by-Step Mathematical Working): [1 Mark]

First, calculate the number of atoms ($N$):

$$N = \frac{\text{mass}}{\text{molar mass}} \times N_A = \frac{1}{239} \times 6.023 \times 10^{23}$$

Now, calculate total energy ($E_{total}$):

$$E_{total} = \left( \frac{6.023 \times 10^{23}}{239} \right) \times 180 \text{ MeV}$$ $$E_{total} \approx 2.52 \times 10^{21} \times 180 \text{ MeV}$$ $$E_{total} \approx 4.536 \times 10^{23} \text{ MeV}$$

Step 3 (Final Concluded Answer): [0.5 Mark]

The total energy released is approximately $4.54 \times 10^{23} \text{ MeV}$.

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💡 EL10 Concept Insight: Think of it like a giant pile of tiny batteries; since one atom releases a huge burst of energy when it breaks, having a whole gram of them means you are multiplying that tiny burst by trillions of trillions of atoms, resulting in a massive amount of power!