What is the correct order of decreasing size of the following ions? multiple choice ca2+ > k+ > cl– > p3– k+ > cl– > ca2+ > p3– p3– > cl– > k+ > ca2+ correct k+ > cl– > p3– > ca2+ none of these choices are correct.

> > >

Explanation:

Isoelectronic specie are defined as the molecules which have the same number of electrons.

Atomic number of calcium is 20 and thus has 20 electrons. is formed by loss of 2 electrons and thus has 18 electrons.

Atomic number of potassium is 19 and thus has 19 electrons.  is formed by loss of 1 electron and thus has 18 electrons.

Atomic number of chlorine is 17 and thus has 17 electrons.  is formed by gain of 1 electron and thus has 18 electrons.

Atomic number of phosphorous is 15 and thus has 13 electrons. is formed by gain of 3 electrons and thus has 18 electrons.

As the number of electrons are same , the more is the nuclear charge i.e. the number of protons , more will the force of attraction towards the nuclei and thus smaller will be the radii and vice versa.

Thus, order of decreasing ionic radii for the given ions is as follows.

> > >

- calcium has greater affinity to bond with electron receptors than hydrogen does and hence, it has the ability to replace hydrogen in most of its compounds.

- lithium has 2 valence electrons in the product because it can make only 1 bond with hydrogen. beryllium has 4 valence electrons in the product because it can only make 2 bonds. it has fewer electrons than neon and can react with electron donors. each hydrogen has 2 valence electrons, the same as helium.

- the covalent bond formed between carbon and hydrogen is polar because carbon is more electronegative than hydrogen and it attracts the bonded electron pair closer to itself, thus giving hydrogen a partial positive charge.

- a hydrogen bond is a relatively weak bond that hydrogen atoms make with the electronegative atoms nitrogen, oxygen or fluorine.

so the best choice is a.) 2 calcium (ca) atoms