Which of the following is not an alkali?

Correct answer: (d) C₂H₅OH

Explanation

An alkali is a base that dissolves in water and gives hydroxide ions (OH⁻):

• NaOH and KOH are strong alkalis;
• NH₄OH (ammonia solution) is a weak alkali.

Ethanol (C₂H₅OH) has an –OH group, but it is an alcohol: the O–H group is joined to carbon by a covalent bond and does not release OH⁻ ions in water. So ethanol is not an alkali, and its solution is neutral.