Assertion (A): Chlorine with atomic number 17 is placed in group 17 and period 3.
Reason (R): The number of shells signifies a period, while the number of valence electrons indicates the group.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Both A and R are true but R is not the correct explanation of A.
Explanation — Chlorine, a halogen with atomic number 17 has valency -1 so, it is placed in group 17. Chlorine has total three shells- K, L and M. So, it is placed in period 3. Hence, the assertion (A) is true.
The number of shell(s) in an atom signifies in which period it is placed and number of valence electrons indicates its group. Hence reason (R) is true.
But, reason (R) does not explain why chlorine is placed in group 17 and period 3. Hence reason (R) is not the correct explanation of assertion (A).