Question

The wavelength of the first line of Lyman series for hydrogen atom is equal to that of the second line of Balmer series for a hydrogen like ion. The atomic number $Z$ of hydrogen like ion is

• A. 3
• B. 4
• C. 1
• D. 2

Answer 1

Answer: (D)

2

Answer 2

$\frac{1}{\lambda}= R Z^{2}\left(\frac{1}{ n _{1}^{2}}-\frac{1}{ n _{2}^{2}}\right)$
$R (1)^{2}\left(\frac{1}{1^{2}}-\frac{1}{2^{2}}\right)= R Z ^{2}\left(\frac{1}{2^{2}}-\frac{1}{4^{2}}\right)$
$Z =2$