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.

explanation:

i think option no d is the correct answer

  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-