First and second ionization enthalpies of lithium are $520 \text{ kJ mol}^{-1}$ and $7297 \text{ kJ mol}^{-1}$ respectively. Energy required to convert $3.5 \text{ mg}$ lithium $(g)$ into $Li^{2+}(g)$ [$Li(g) \rightarrow Li^{2+}(g)$] is . . . . . . $\text{kJ}$. (nearest integer) [Molar mass of $Li = 7 \text{ g mol}^{-1}$]

• A
  $5$
• B
  $4$
• C
  $3$
• D
  $2$