Question

A compound is a pure substance made up of two or more elements combined chemically in a ________ proportion by ________:
(A) variable, volume
(B) definite, mass
(C) constant, weight
(D) Both B and C

Answer 1

Hint: The compound formed by the chemical bonding between its constituent elements which are taken in a fixed amount to form the stable substance. This gives us a specific formula for a compound.

Complete step by step solution:
Firstly, a substance is called a pure substance which has a constant composition throughout the system. Its properties also remain uniform, thus a fixed melting and boiling point.
Also, the pure substance is made up of a single type of an atom or molecule. Such that they cannot be separated into its constituent elements by physical means.
Thus, a compound is a substance which is made up of two or more different atoms in a fixed ratio, that are chemically bonded. This makes the compound to have properties different from its constituting atoms. Therefore, a compound is a pure substance.
The chemical bonding present between the atoms of a compound can be either ionic or covalent in nature. Thus, giving the chemical formula of the compound which represents the ratio at which the constituting elements are present.

Therefore, a compound is a pure substance made up of two or more elements combined chemically in a definite proportion by mass. That is, option (B)- definite, mass.

Note: The compound can be broken down into its constituent elements by chemical means into atoms or molecules. This makes the molecule to be the smallest entity of a compound, which still retains its properties.
For example, in a compound of sodium chloride, it consists of sodium and chlorine atoms (as elements) whereas it is made up of sodium chloride molecules.