Ground-state $He X^{+}$ is to be ionised by a photon. Take the ionisation energy of hydrogen as 13.6 eV and $h c = 1240 eV nm$ . The maximum wavelength of radiation that can ionise $He X^{+}$ is

A $45.6 nm$
B $11.4 nm$
C $91.2 nm$
D $22.8 nm$

Answer: D

For

He X^{+}

(

Z = 2

), IE = 13.6 x 4 = 54.4 eV. Wavelength = 1240/54.4 = 22.8 nm. Using 13.6 eV (hydrogen) would give 91.2 nm, and the other options come from wrong factors of

Z

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Ground-state HeX+ is to be ionised by a photon. Take the ionisation energy of hydrogen as 13.6 eV and hc=1240 eV nm. The maximum wavelength of radiation that can ionise HeX+ is

Answer: D

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Ground-state $He X^{+}$ is to be ionised by a photon. Take the ionisation energy of hydrogen as 13.6 eV and $h c = 1240 eV nm$ . The maximum wavelength of radiation that can ionise $He X^{+}$ is