Step 1: What is dettol.
Dettol is a well known antiseptic liquid used to clean wounds and surfaces. We must find its main ingredient.
Step 2: Name the active part.
The main active part of dettol is chloroxylenol. This is a phenol type compound that kills germs.
Step 3: The second part.
Dettol also has terpineol mixed in. Terpineol helps the chloroxylenol work and gives a pleasant smell.
Step 4: Rule out bithionol.
Bithionol is added to soaps as an antiseptic, but it is not the main part of dettol.
Step 5: Rule out iodine and phenol.
Iodine is used in tincture of iodine, a different antiseptic. Plain phenol is too harsh and is not the main part of dettol.
Step 6: Final choice.
So the main constituents of dettol are chloroxylenol and terpineol.\[ \boxed{\text{Chloroxylenol and terpineol}} \]