Answer:
Immune system
Explanation:
Rheumatoid arthritis is an autoimmune disease. Normally, your immune system helps protect your body from infection and disease. In rheumatoid arthritis, your immune system attacks healthy tissue in your joints. It can also cause medical problems with your heart, lungs, nerves, eyes and skin.
Number 1 goes with obsolete
Number 2 goes with molecular structure
Number 3 goes with ion
Number 4 goes with isotope
Number 5 goes with residue
Number 6 goes with anthracite
Number 7 goes with electrolysis
Number 8 goes with chemical formula
Number 9 goes with subscript
Number 10 goes with bituminous
Number 11 goes with electroplate
Number 12 goes with structure