The work function $\phi_0$ of a metal is the minimum energy required for an electron to escape its surface. Which of the following is the correct unit and order of magnitude for $\phi_0$ of common metals?

1. NCERT Ch 11 §11.2 defines $\phi_0$ as the minimum energy required by an electron to escape the metal surface. Energy is measured in joules (SI) or electron-volts (atomic / nuclear). 2. The relation between the two is $1\,\text{eV} = 1.602\times 10^{-19}\,\text{J}$. 3. For common metals the work function is in the range $2$–$5\,\text{eV}$, i.e. $\sim 3\times 10^{-19}\,\text{J}$, so the joule order of magnitude is $10^{-19}\,\text{J}$. 4. Option B is internally inconsistent: $10^{-19}\,\text{eV}$ is far below thermal energy at room temperature ($\sim 25\,\text{meV}$). Watts (option C) and newtons (option D) are not energy units. _Source: NCERT Class 12 Physics Part 2, Ch 11 "Dual Nature of Radiation and Matter", §11.2 (Electron Emission), p. 1 ¶3._