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Question:

Given the value of Rydberg's constant is 107 m⁻¹, the wave number of the last line of the Balmer's series in hydrogen spectrum will be:

0.5×10⁷m⁻¹

0.25×10⁷m⁻¹

2.5×10⁷m⁻¹

0.025×10⁴m⁻¹

Solution:

We know that :
1/λ = R(1/n₁² - 1/n₂²)
For last line Balmer's series ,n₁=2,n₂=∞
1/λ = 10⁷(1/2² - 1/∞²) = 0.25×10⁷m⁻¹