AIIMS 2018 Physics Bohr's Model MCQ Question

In the second orbit of helium (He), which has two electrons, the velocity of an electron can be calculated using the Bohr model formula for hydrogen-like atoms: $v_n = Z \cdot \frac{e^2}{4 \pi \epsilon_0 \hbar} \cdot \frac{1}{n}$, where $Z$ is the atomic number (2 for helium), $e$ is the elementary charge, $\epsilon_0$ is the permittivity of free space, $\hbar$ is the reduced Planck's constant, and $n$ is the principal quantum number (2 for the second orbit). Substituting the values yields a velocity of approximately $2.1 \times 10^6 \, \text{m/s}$, confirming option (A) as correct.

Options (B), (C), and (D) are incorrect as they either overestimate or underestimate the electron's velocity based on the fundamental principles of quantum mechanics and the specific parameters for helium's electron configuration.