Question

which of the following is an isoelectronic series?

b^{5 - },sr^{4 - },as^{3 - },te^{2 - }

f^{ - },cl^{ - },br^{ - },i^{ - }

s,cl,ar,k

si^{2 - },p^{2 - },s^{2 - },cl^{2 - }

o^{2 - },f^{ - },ne,na^{ + }

Explanation:

Step1: Recall the definition of isoelectronic series

Isoelectronic species have the same number of electrons.

Step2: Calculate the number of electrons for each option

• Option 1: \(B^{5 -},Sr^{4 -},As^{3 -},Te^{2 -}\)
• \(B\) has \(5\) protons. \(B^{5 -}\) has \(5 + 5=10\) electrons.
• \(Sr\) has \(38\) protons. \(Sr^{4 -}\) has \(38+4 = 42\) electrons.
• \(As\) has \(33\) protons. \(As^{3 -}\) has \(33 + 3=36\) electrons.
• \(Te\) has \(52\) protons. \(Te^{2 -}\) has \(52+2 = 54\) electrons. Not isoelectronic.
• Option 2: \(F^{-},Cl^{-},Br^{-},I^{-}\)
• \(F\) has \(9\) protons. \(F^{-}\) has \(9 + 1=10\) electrons.
• \(Cl\) has \(17\) protons. \(Cl^{-}\) has \(17+1 = 18\) electrons.
• \(Br\) has \(35\) protons. \(Br^{-}\) has \(35 + 1=36\) electrons.
• \(I\) has \(53\) protons. \(I^{-}\) has \(53+1 = 54\) electrons. Not isoelectronic.
• Option 3: \(S,Cl,Ar,K\)
• \(S\) has \(16\) electrons (neutral atom).
• \(Cl\) has \(17\) electrons (neutral atom).
• \(Ar\) has \(18\) electrons (neutral atom).
• \(K\) has \(19\) electrons (neutral atom). Not isoelectronic.
• Option 4: \(Si^{2 -},P^{2 -},S^{2 -},Cl^{2 -}\)
• \(Si\) has \(14\) protons. \(Si^{2 -}\) has \(14+2 = 16\) electrons.
• \(P\) has \(15\) protons. \(P^{2 -}\) has \(15 + 2=17\) electrons.
• \(S\) has \(16\) protons. \(S^{2 -}\) has \(16+2 = 18\) electrons.
• \(Cl\) has \(17\) protons. \(Cl^{2 -}\) is not a common ion ( \(Cl^{-}\) is common). Not isoelectronic.
• Option 5: \(O^{2 -},F^{-},Ne,Na^{+}\)
• \(O\) has \(8\) protons. \(O^{2 -}\) has \(8+2 = 10\) electrons.
• \(F\) has \(9\) protons. \(F^{-}\) has \(9 + 1=10\) electrons.
• \(Ne\) has \(10\) electrons (neutral atom).
• \(Na\) has \(11\) protons. \(Na^{+}\) has \(11-1 = 10\) electrons. All have \(10\) electrons.

Answer:

\(O^{2 -},F^{-},Ne,Na^{+}\)