Which of the following compounds contains a double bond? methane ethene ammonia chlorine

Methane (CH4) does not contain a double bond. Methane consists of a single carbon atom that shares single bonds with four hydrogen atoms.  
Ethene (C2H4) contains a double bond. The molecule consists of two carbon atoms which are double bonded. Each of the carbon atoms shares singles bonds with two hydrogen atoms. 
 Ammonia (NH3) does not contain a double bond. Ammonia consists of a single nitrogen atom that shares single bonds with three hydrogen atoms. A lone pair of electrons exists on the nitrogen atom. 
 Chlorine (Cl2) does not contain a double bond. The molecule consists of two chlorine atoms that share a single bond. Three pairs of lone electrons reside on each of the chlorine atoms.

Tolerance to high levels of salinity