Calculation of wavelength of electron in first excited state
Radius of n‌th ‌ orbit
r‌=r0n2=0.53n2×Å
‌=0.53×4Å
‌=2.12Å [∵ Here n=2]
For an electron revolving in n‌th ‌ orbit, according to de Broglie relation
‌2πrn=nλ‌, ‌
‌‌ For ‌1‌st ‌‌ excited state ‌n=2
‌2×3.14×2.12×10−10=2λ
‌λ=3.14×2.12×10−10
‌=6.67Å