Question

Substance which is weakly repelled by a magnetic field is

• A. ${{O}_{2}}$
• B. ${{H}_{2}}O$
• C. $Cr{{O}_{2}}$
• D. $F{{e}_{3}}{{O}_{4}}$

Answer 1

Answer: (B)

${{H}_{2}}O$

Answer 2

${{O}_{2}}$ molecule is paramagnetic and the presence of two unpaired electrons in the
$\overset{*}{\mathop{\pi }}\,(2{{p}_{x}})$ or $\overset{*}{\mathop{\pi }}\,(2{{p}_{y}})$
molecular orbitals accounts for its paramagnetic nature.
Similary in $Cr{{O}_{2}},$
$F{{e}_{3}}{{O}_{4}}$ and $ZnF{{e}_{2}}{{O}_{4}},$
the d-orbitals of transition elements are not fulfilled and have unpaired electrons and hence, are paramagnetic. Whereas, ${{H}_{2}}O$ is diamagnetic because of the presence of all paired electrons and hence repelled by magnetic field.