Calculate the wavelength for the emission transition if it starts from the orbit having radius 1.3225 nm and ends at the one having 211.6 pm. Name the series to which this transition belongs and the region of the spectrum.

The radius of nth orbit of H-like species is given by the expression 0.529n²/Z Å or 52.9n²/Z pm.
r₁ = 1.3225 nm = 1322.5 pm = 52.9n₁²/Z pm. (1)
r₂ = 211.6 pm = 52.9n₂²/Z pm. (2)
Dividing (1) by (2), we get
r₁/r₂ = 1322.5/211.6 = n₁²/n₂²
n₁²/n₂² = 6.25 ⇒ n₁/n₂ = 2.5
n₂ = 5, n₁ = 2.
The transition is in Balmer series.
ν = 1.097 × 10⁷(1/2² - 1/5²) = 1.097 × 10⁷ × 0.21 m⁻¹
λ = 1/ν = 1/(2.3037 × 10⁶) m = 434 × 10⁻⁹ m or 434 nm
The transition lies in the visible region.