Question

Two chemical substances $\mathrm{A}$ and $\mathrm{B}$ combine to form a product $\mathrm{C}$ which contains both $\mathrm{A}$ and $\mathrm{B}$:

$\mathrm{A}+\mathrm{B}\to \mathrm{C}$

$\mathrm{A}$ has fixed composition and can be broken down into simpler substances by simple chemical reactions but $\mathrm{B}$ cannot. Which of the following statements concerning $\mathrm{A}$, $\mathrm{B}$ and $\mathrm{C}$ are correct?

(i) $\mathrm{A}$ and $\mathrm{B}$ are compounds

(ii) $\mathrm{A}$ and $\mathrm{B}$ are elements

(iii) $\mathrm{A}$ is a compound and $\mathrm{B}$ is an element

(iv) $\mathrm{C}$ is a compound

(v) $\mathrm{C}$ has fixed composition

(vi) $\mathrm{A}$ and $\mathrm{C}$ are compounds.

Answer 1

1. Elements: A pure substance that can neither be reduced further nor can be formed by physical or chemical methods and is made up of the same type of atoms.
2. Compounds: It is a substance that is formed by mixing two or more elements in a defined ratio.
3. Mixtures: It is a substance made by mixing two or more pure substances in an undefined proportion.
4. Since it is given in the question that $\mathrm{A}$ has a fixed composition and can be broken down into simpler substances by simple chemical reactions, it clearly reflects that $\mathrm{A}$ is a compound.
5. Whereas $\mathrm{B}$ cannot be broken down further into simpler substances make it clear that $\mathrm{B}$ is an element.
6. Reaction between $\mathrm{A}$ which is a compound and $\mathrm{B}$ which is an element will itself gives a compound having a fixed composition. Therefore, $\mathrm{C}$ is also a compound.

For instance,$$\begin{gathered} \mathrm{Compound}+\mathrm{Element}\to \mathrm{Compound} \\ {\mathrm{SO}}_2\left(l\right)+\frac{1}{2}{\mathrm{O}}_2\left(\mathrm{g}\right)\to {\mathrm{SO}}_3\left(\mathrm{l}\right) \\ (\mathrm{Sulphur}\mathrm{dioxide})(\mathrm{Oxygen}\mathrm{gas})(\mathrm{Sulphur}\mathrm{trioxide}) \end{gathered}$$

Based on the above interpretations correct statements are:

(iii) $\mathrm{A}$ is a compound and $\mathrm{B}$ is an element

(iv) $\mathrm{C}$ is a compound

(v) $\mathrm{C}$ has a fixed composition

(vi) $\mathrm{A}$ and $\mathrm{C}$ are compounds

Therefore, correct statements are (iii), (iv), (v) and (vi).