Which example specifically illustrates obligatory Rule 2?

Rules of Hamzated Forms: Lightening, Substitution, Elision and Short Paradigms

• يَسْأَلُ → يَسَلُ
• بُؤْسٌ → بُوسٌ
• أَأْمَنَ → آمَنَ
• سُؤَالٌ → سُوَالٌ