In a regular octahedral molecule, $MX_6$ the number of X–M–X bonds at $180^\circ$ is :-
A
Two
B
Six
C
Four
D
Three
The answer is D.
Solution
In a regular octahedron, the six X atoms lie along the $+x$, $-x$, $+y$, $-y$, $+z$ and $-z$ axes around M. An X–M–X angle of $180^\circ$ occurs only between two X atoms on opposite ends of the same axis (trans positions). The pairs are: $+x$ and $-x$, $+y$ and $-y$, $+z$ and $-z$. All other pairs of X atoms (cis pairs, 12 in number) make $90^\circ$ angles. So the number of X–M–X bonds at $180^\circ$ is three.
ConceptTrans bond angles in octahedron
Chemical Bonding and Molecular Structure in past papers
108 questions from this chapter have appeared across 27 exam years.
