When electromagnetic radiation of wavelength $300 \ nm$ falls on the surface of a metal,electrons are emitted with the kinetic energy of $1.68 \times 10^5 \ J \ mol^{-1}$. What is the minimum energy needed to remove an electron from the metal? $(h = 6.626 \times 10^{-34} \ J \ s, c = 3 \times 10^8 \ m \ s^{-1}, N_A = 6.022 \times 10^{23} \ mol^{-1})$

• A
  $2.31 \times 10^6 \ J \ mol^{-1}$
• B
  $3.84 \times 10^4 \ J \ mol^{-1}$
• C
  $3.84 \times 10^{-19} \ J \ mol^{-1}$
• D
  $2.31 \times 10^5 \ J \ mol^{-1}$