Cho $4,48$ lit hon hop $X$ (dktc) gom 2 HC mach ho, loi tu` tu` qua binh chua $1,4$ lit dd $Br_2 0,5M$ (khong no, bi giu lai). Sau khi pu hoan toan so mol $Br_2$ giam di 1 nua va khoi luong binh tang them $6,7$ g. CTPT cua 2 HC la: $A.C_2H_2;C$ $B,C_2H_2;C_4H_8$
$C. C_3H_4; C_4H_8$ $D.C_2H_2;C_3H_6$