MCQ
The shortest wavelength of hydrogen atom in Lyman series is $\lambda$. The longest wavelength in Balmer series of $He ^{+}$is
  • A
    $\frac{5}{9 \lambda}$
  • $\frac{9 \lambda}{5}$
  • C
    $\frac{36 \lambda}{5}$
  • D
    $\frac{5 \lambda}{9}$

Answer

Correct option: B.
$\frac{9 \lambda}{5}$
b
For $H : \frac{1}{\lambda}= R _{ H } \times 1^2\left(\frac{1}{1^2}-\frac{1}{\infty^2}\right)$

$\frac{1}{\lambda_{ He ^{+}}}= R _{ H } \times 2^2 \times\left(\frac{1}{4}-\frac{1}{9}\right)$

From $(1)$ and $(2)$ $\frac{\lambda_{ He ^{+}}}{\lambda}=\frac{9}{5}$

$\lambda_{ He ^{+}}=\lambda \times \frac{9}{5}$

$\lambda_{ He ^{+}}=\frac{9 \lambda}{5}$

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