Linked from
The 10 pages that link to Inert-pair effect, each with the reason it gives.
Lead(II) ionRelated: It helps stabilize lead’s +2 state relative to its +4 state.
PnictogenRelated: It helps stabilize lower oxidation states in heavier pnictogens such as bismuth.
Boron groupRelated: It helps explain why the +1 oxidation state becomes more stable down group 13.
Carbon groupRelated: It helps explain why lead commonly forms +2 compounds rather than +4 compounds.
ThalliumRelated: This effect helps explain why thallium’s +1 state is more stable than +3.