Match the mass quantities in List-I with their corresponding energy...

According to Einstein's mass-energy equivalence, $E = mc^2$.

(A) For $m = 1 \text{ kg}$:
$E = 1 \times (3 \times 10^8)^2 = 9 \times 10^{16} \text{ J}$. (Matches III)

(B) For $m = 1 \text{ mg} = 10^{-6} \text{ kg}$:
$E = 10^{-6} \times (3 \times 10^8)^2 = 9 \times 10^{10} \text{ J}$. (Matches IV)

(C) $1 \text{ atomic mass unit (u)}$ is standardly equivalent to $931.5 \text{ MeV}$. (Matches I)

(D) The rest mass energy of an electron is standardly $0.511 \text{ MeV}$. (Matches II)

Therefore, the correct matching is (A)-(III), (B)-(IV), (C)-(I), (D)-(II).

Answer: (A)-(III), (B)-(IV), (C)-(I), (D)-(II)