Q67 / 200 · NEET 2009 (Screening) · Chemistry

In the case of alkali metals, the covalent character decreases in the order

  • A
    $\mathrm{MCl}>\mathrm{MI}>\mathrm{MBr}>\mathrm{MF}$
  • B
    $\mathrm{MF}>\mathrm{MCl}>\mathrm{MBr}>\mathrm{MI}$
  • C
    $\mathrm{MF}>\mathrm{MCl}>\mathrm{MI}>\mathrm{MBr}$
  • Correct answer
    D
    $\mathrm{MI}>\mathrm{MBr}>\mathrm{MCl}>\mathrm{MF}$

Solution

Key Idea According to Fajan's rule, Covalent character $\propto \frac{1}{\text { size of cation }}$ $\propto$ In the given options, cation is same but anions are different. Among halogens the order of size is $$ \mathrm{F} < \mathrm{Cl} < \mathrm{Br} < \mathrm{I} $$ $\therefore$ Order of covalent character is $$ \mathrm{MI}>\mathrm{MBr}>\mathrm{MCl}>\mathrm{MF} $$

Hence, the correct answer is option: 'D'.

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