`color{#42bfb5}\text{H}color{#55c5bc}\text{uy}color{#68ccc4}\text{e}color{#7bd2cb}\text{n}`

`@ 100^@C`

`m_(CuCl_2)=(55.120)/(100+120)=30(g)`

`m_(H_2O)=55-30=25(g)`

Gọi số mol tinh thể tách ra là `x (mol)`

`=> m_(CuCl_2)=135x(g)`

`m_(H_2O)=36x(g)`

`@20^@C`

`m_(CuCl_2)=30-135x (g)`

`m_(H_2O)=25-36x (g)`

ta có tỉ lệ:

`(30-135x)/(25-36x)=73/100`

`=>x~~0,10807`

`=> m_(CuCl_2.H_2O)=0,10807.171=18,48`

`to` Chọn `B`