An answer that makes reference to the following point:
- chlorine has non-bonding electrons in its outer shell which repel the bonding pairs (of electrons)
Allow any answer referring to lone or non-bonding electrons, including just a single electron and referring to repulsion or repulsive forces with bonding pairs and/or lone pairs e.g. there are lone pairs of electrons and lone pair repulsion is greater than bond pair repulsion
Ignore the lone pairs on oxygen repel Ignore just chlorine dioxide minimises repulsion between electrons
Do not award the lone pair of electrons repel the oxygen atoms