The speed of the electron in $n=3$ orbit of $He^+$ ion would be

(given $k= 9 × 10^9 Nm^2C^{-2}; e = 1.6 × 10^{-19} C; h = 6.63 × 10^{-34} Js$)

$1.46 × 10^6\, ms^{-1}$

The correct answer is Option (1) → $1.46 × 10^6\, ms^{-1}$

Formula: $v_n = \frac{Z \alpha c}{n}$

For He$^+$, $Z = 2,\ n = 3,\ \alpha = \frac{1}{137},\ c = 3 \times 10^8 \ \text{m/s}$

$v_n = \frac{2}{3} \cdot \frac{1}{137} \cdot 3 \times 10^8$

$v_n = 1.46 \times 10^6 \ \text{m/s}$

Answer: $1.46 \times 10^6 \ \text{m/s}$