Question

Assertion :The $5^{th}$ period of periodic table contains 18 elements not 32. Reason: $n=5,l=0,1,2,3$. The order in which the energy of available orbitals $4d,5s$ and $5p$ increases in $5s<4d<5p$ and the total number of orbitals available are 9 and thus 18 electrons can be accommodated.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but 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 Reason is the correct explanation for Assertion

The fifth period of periodic table contains 18 elements not 32 as

$n=5$

$l=0to(n-1)$

$l=0-4;0,1,2,3,4$

In fifth period the starting orbital is $4s$. So 4s is filled by 2 electrons. $4p$ by 6 electrons and $4d$ by 10 electrons. So total 18 electrons or elemnts can be there.