Which of the following property does not describe a compound?
(d) It is mixed in any proportion by mass.
Explanation for correct option:
(D) It is mixed in any proportion by mass.
Compounds are always mixed in a fixed proportion by mass.
Therefore, option (d) is not a characteristic of the compound.
Explanation for incorrect options:
(A) It is composed of two or more elements
A compound is formed when two or more elements are combined chemically with one another in a fixed proportion.
(B) It is a pure substance
A compound is composed of only one type of molecule. Molecules are composed of two or more types of atoms. This makes the compound a pure substance.
(C) It cannot be separated into constituents by physical means
As the elements are chemically combined to form compounds, separating them by the physical method is impossible. Its constituents can only be separated by chemical or electrochemical methods.
Therefore, options (A), (B), and (C) are the characteristics of the compound.
Hence, option (D) is correct. The compound is not mixed in any proportion by mass.