Ordering acetic acid and nitrous acid by increasing strength gives:

1. Relative acid strength follows the size of the ionisation constant. 2. The ionisation constants increase from the first to the last of the listed equations. 3. That indicates the relative acid strength increases in the order acetic acid, then nitrous acid. 4. So nitrous acid is the stronger of the two. 5. A larger Ka always means a more fully ionised, and therefore stronger, acid. _Source: OpenStax Chemistry 2e (CC BY 4.0), Ch 14 'Acid-Base Equilibria', sections 14.1-14.7_