Energy of an electron is given by E=-2.178×10-18 JZ2n2Wavelength of light required to excite an electron in an hydrogen atom from level n = 1 to n = 2 will beh=6.62×10-34Js and c=3.0×108 ms-1

Given, in the question E=-2.178×10-8 JZ2n2For hydrogen Z = 1, So,  E1=-2.178×10-18 J112E2=-2.178×10-18 J122 Now, E1-E2 i.e.  ΔE=2.178×10-18112-122=hcλ2.178×10-18112-122=6.62×10-34×3.0×108λ∴ λ≈1.21×10-7 m