You can download from this page
A/l Chemistry 2020 paper sinhala medium (MCQ+ Structured+Essay)
A/l Chemistry 2020 paper Sinhala Medium Marking Scheme
A/l Chemistry 2020 English Medium Paper (MCQ+ Structured+Essay)
A/l Chemistry 2020 English Medium Marking Scheme
Source- Department of examination Sri Lanka
You also can download,
2019 G.C.E A/l Chemistry paper with marking scheme
2021 G.C.E A/l Chemistry paper with marking scheme