<span>Explanation: </span> <span /><span /><span> The term isoelectronic means same number of electrons. </span><span />
<span>Then you need to count the number of electrons in the given species NO₂⁻. </span><span />
<span>You have to count the number of electrons of N (nitrogen) atoms, the number of electrons of two O (oxygen) atoms, and the adjust for the negative charge of the ions.
</span><span>The atomic number of N is 7, meaning that each atom has 7 protons and 7 electrons.</span> <span /><span> The atomic number of O is 8, meaning that each atom has 8 protons and 8 electrons. </span><span />
<span>The negative charge of the ion means that it has one extra electron, which is the responsible for the negative charge. </span><span />
<span>Therefore the total number of electrons of the ion NO₂⁻ is 7 + 2 (8) + 1 = 24. </span><span />
<span>Note that that 24 = 3 x 8, so 24 is the number of electrons in 3 atoms of oxygen. </span><span />
<span>The moleucle O₃ is an allotrope of the oxygen. (an allotrope is a a form of an element with different structure and physical properties in the same physical state). </span><span />
<span>Therefore, the allotrope of oxygen isoelectronic with NO₂⁻ is O₃ (ozone)</span>
