Question

Assertion: Elements present in the group show same valency.

Reason: Elements present in a group have same number of electrons in the valence shells of their atoms.

Mark the correct choice as

• A. Both assertion and reason are correct and the reason is the correct explanation of assertion.
• B. Both assertion and reason are correct but the reason is not the correct explanation of assertion.
• C. Assertion is correct but the reason is incorrect.
• D. Assertion is incorrect but reason is correct.

Answer 1

The correct option is A

Both assertion and reason are correct and the reason is the correct explanation of assertion.

Explanation for assertion statement:

1. Valency is the combining capacity of an atom, it can be understood as the total number of electrons lost, shared or accepted by an atom to form a bond in a compound.
2. If we go down the group, valency remains constant. For example, the valency of all the elements from group 1 (alkali metals) is 1.

Explanation for reason statement:

1. All the elements in a group have the same valence shell electronic configuration. For example, group 1 has the electronic configuration of

$$\begin{gathered} {}_{3}Li=2,1 \\ {}_{11}Na=2,8,1 \\ {}_{19}K=2,8,8,1 \\ {}_{37}Rb=2,8,18,8,1etc. \end{gathered}$$

2. All of them here have 1 electron in their outermost shell. They all donate their only outermost electron to form an ionic bond, hence the valency is 1 for the group.

Hence, A) Both assertion and reason are true, reason is the correct explanation of assertion.