insoluble
adjective uk/ɪnˈsɒl.jə.bəl/ us/ɪnˈsɑːl.jə.bəl/
(PROBLEM)
(US also insolvable)（问题）无法解决的
(of a problem) so difficult that it is impossible to solve
Traffic congestion in large cities seems to be an insoluble problem. 大城市的交通堵塞问题似乎无法解决。
(SUBSTANCE)
（物质）不能溶解的
(of a substance) impossible to dissolve
These minerals are all insoluble in water. 这些矿物质都不溶于水。