Which of the following property does not describe a compound?

Question

Accepted Answer

Option 4 is the correct answer because it states that a compound "is mixed in any proportion by mass," which does not accurately describe a compound. Compounds have a fixed composition with elements combined in definite proportions by mass. This means that the ratio of the elements in a compound is always constant, regardless of the amount of the compound. For example, water (H₂O) is always composed of hydrogen and oxygen in a 2:1 ratio by mass.

Now, let's explain why each of the other options is incorrect:

1. **Option 1: It cannot be separated into its constituents by physical means.**
   - This statement is true for compounds. Compounds are chemically bonded, and their constituent elements cannot be separated by physical means such as filtration or distillation. Instead, chemical reactions are required to break the bonds and separate the elements.

2. **Option 2: It is composed of two or more elements.**
   - This is also true for compounds. By definition, a compound is a substance formed when two or more elements are chemically bonded together. For example, sodium chloride (NaCl) is a compound composed of sodium and chlorine.

3. **Option 3: It is a pure substance.**
   - This statement is correct for compounds. A pure substance has a uniform and definite composition, and compounds fit this description because they consist of molecules that are all identical in composition and structure.

In summary, Option 4 is the correct answer because it inaccurately describes a compound as being mixed in any proportion by mass, which contradicts the fixed and definite composition that characterizes compounds. The other options correctly describe properties of compounds, reinforcing why Option 4 is the only incorrect statement.