Which of the following is least soluble in water?
(A) C2H6
(B) CH3OH
(C) CH3NH2
(D) C6H5OH

To determine which substance is least soluble in water, we can look at their chemical structures and solubility properties.

A.
C
2
H
6
C
2
​
H
6
​
(Ethane) - This is a nonpolar molecule composed of only carbon and hydrogen atoms. Nonpolar molecules are typically not soluble in water.

B.
CH
3
OH
CH
3
​
OH (Methanol) - This is a polar molecule due to the presence of the hydroxyl (OH) group. Polar molecules tend to be soluble in water due to their ability to form hydrogen bonds with water molecules.

C.
CH
3
NH
2
CH
3
​
NH
2
​
(Methylamine) - This molecule is polar due to the amino (NH2) group. It can form hydrogen bonds with water molecules and is thus soluble in water.

D.
C
6
H
5
OH
C
6
​
H
5
​
OH (Phenol) - This molecule contains a hydroxyl (OH) group attached to a benzene ring. It can participate in hydrogen bonding with water molecules and is soluble in water to some extent.

Based on this analysis, the least soluble substance in water is option A,
C
2
H
6
C
2
​
H
6
​
(Ethane), as it is nonpolar and lacks the ability to form significant interactions with water molecules.