The energy equivalent of $$1$$ g of substance is :

Using Einstein's mass-energy equivalence: $$E = mc^2$$.

Given: $$m = 1$$ g = $$10^{-3}$$ kg, $$c = 3 \times 10^8$$ m/s.

$$E = 10^{-3} \times (3 \times 10^8)^2 = 10^{-3} \times 9 \times 10^{16} = 9 \times 10^{13} \text{ J}$$

Converting to MeV: $$1$$ MeV = $$1.6 \times 10^{-13}$$ J.

$$E = \frac{9 \times 10^{13}}{1.6 \times 10^{-13}} = \frac{9}{1.6} \times 10^{26} = 5.625 \times 10^{26} \approx 5.6 \times 10^{26} \text{ MeV}$$

The correct answer is Option 2: $$5.6 \times 10^{26}$$ MeV.