Question

The ratio of speed of electron in $I$ orbit of $H$-atom to $IV$ orbit of $H{e}^{+}$ ion is :

• A. $4$
• B. $5$
• C. $2$
• D. $3$

Answer 1

Answer: (C)

$2$

The speed of electron is given by the expression.
$u=\frac{Z}{n}\times 2.19\times {10}^{8}cm/sec$
The ratio of speed of electron in I orbit of H-atom to IV orbit of $H{e}^{+}$ -ion is
$\frac{Z_H\times n_{He+}}{Z_{He+}\times n_H}=\frac{1\times 4}{2\times 1}=2$