Question

Pure substances are characterized by__________.

• A. Variable properties
• B. Fixed boiling points
• C. Variable melting points
• D. Non-uniform composition

Answer 1

The correct option is B

Fixed boiling points

Explanation for correct answer:-

Option: (B)

• A pure substances are termed as the a single substance.
• Hydrogen, oxygen, nitrogen etc. are some examples of pure substances.
• The physical and chemical properties of pure substances are fixed.
• The pure substances have fixed melting points, boiling points, solubility and density.
• Thus, pure substances are characterized by fixed boiling points.

Explanation for Incorrect answer:-

Options: (A)

• Pure substances have fixed chemical and physical properties.
• Whereas variable properties i.e variable melting points, non-uniform composition and variable properties are properties of mixtures.
• Therefore, this option is incorrect.

Options: (C)

• Pure subtances are homogenous containing only one type of atom or molecule.
• They have uniform composition and fixed physical properties such as melting points.
• Pure substances do not posesses Variable melting points.
• Therefore, this option is incorrect.

Options: (D)

• A pure substance is a single substance and it has uniform composition throughout.
• The composition of a pure substance is definite and its composition is same in different parts of the sample.
• Therefore, this option is incorrect.

Therefore, pure substances are characterized by fixed boiling points.