Helium has two electrons in the 1s orbital. when it becomes singly ionized, forming he+,

(a) its spectrum resembles that of the hydrogen spectrum.

(b) the remaining electron is easier to remove.

(c) the nuclear charge has decreased by one.

(d) it has lost one atomic mass unit.

that of the hydrogen spectrum.

(A) its spectrum resembles that of the hydrogen spectrum

Explanation:

Hydrogen has only one electron in it's outermost shell. Its spectrum shows only one electron transition. If the spectrum of He+ is measured, it will closely resemble that of hydrogen since it is also a one electron specie. The electron also occupying a 1s orbital as in hydrogen.

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