Answer:
水 SUI, mizu - water
硼 HOU - Boron
炭 TAN, sumi - charcoal
窒 CHITSU - plug up, obstruct
酸 SAN, su(i) - acid, sour
They all represent chemical elements.
水素 SUISO - Hydrogen
硼素 HOUSO - Boron
炭素 TANSO - Carbon
窒素 CHISSO - Nitrogen
酸素 SANSO - Oxygen