Question

An element A which is a part of common salt and kept under kerosene reacts with another element B of atomic number 17 to give a product C. When an aqueous solution of product C is electrolysed then a compound D is formed and two gases are liberated.
(a) What are A and B?
(b) Identify C and D.
(c) What will be the action of C on litmus solution? Why?
(d) Write formula of the compound formed when element B reacts with an element E having atomic number 5.

Answer 1

(a) Element A is sodium and element B is chlorine.
Sodium is kept under kerosene because it is highly reactive. Element with atomic number 17 is chlorine. Thus, element A is sodium and element B is chlorine.
 
(b) When element A, sodium, reacts with element B, chlorine, it forms a product C, sodium chloride, NaCl.

 

When aqueous solution of sodium chloride is electrolysed, compound D, sodium hydroxide (NaOH), is formed along with the evolution of hydrogen and chlorine gases.

(c) Compound C is sodium chloride. It has no action on litmus solution. Because sodium chloride is a salt, it is neutral in nature and does not show any action with litmus solution.
 
(d) Element B is chlorine. It is in gaseous state at room temperature.
 
(e) The element E with atomic number 5 is boron. When element B, chlorine, reacts with element E, boron, it forms a compound boron trichloride. The formula of the compound formed is BCl₃.

2B + 3Cl₂ → 2BCl₃