Question

Assertion: Ions of elements which occur at the lower positions at electrochemical series are discharged first from a solution.
Reason: According to the preferential discharge theory, out of a number of ions the one which requires least energy will be liberated first at a given substance.
(A)- Both assertion and reason are true and reason is the correct explanation of assertion.
(B)- Both assertion and reason are true but reason is the correct explanation of assertion.
(C)- Assertion is true but reason is false.
(D)- Assertion is false but reason is true
(E)- Both assertion and reason are false

Answer 1

The elements which are placed at the bottom of the electrochemical series are metals and metals require very less energy to ionize. The metals have very low ionization energy. Due to very low ionization energy, they easily form ions. So, the position of metals in the electrochemical series determine their ability to form ions in a solution.

Complete answer:
Let’s look at the answer to this question:
The elements which are present at the bottom of the electrochemical series are metals. Metals easily form metal ions by releasing electrons. This is because metals have very low ionization enthalpy in comparison to non-metals which are present at higher positions.
So, the statement given in assertion is true.
Now, according to preferential discharge theory, out of all the metal ions present in the solution the metal ion which has least energy will be discharged first.
This happens as metals have negative reduction potential and easily forms ions at low energy and can be discharged at the electrode.
So, the statement given in assertion is true and explains the assertion statement also.

Hence, the answer for the given question is option (A).

Note: The electrochemical series is arranged in increasing order of reduction potential. The lesser the value of reduction potential the more is the tendency to form cation. This means that metals which have low reduction potential have a high tendency to lose electrons and form cations. They are also known as good reducing agents.