Question

Statement I: The $5^{th}$ period of the periodic table contains 18 elements and not 32.
Statement II: $n=5,l=0,1,2and3$. The order in which the energy of the orbitals 4d, 5s and 5p increases is $5s<4d<5p$. The total number of orbitals available are 9 and thus, 18 electrons can be accomodated.

• A. Both the statements are true and Statement II is a correct explanation of Statement I
• B. Both the statements are true and Statement II is not a correct explanation of Statement I
• C. Statement (I) is true and Statement (II) is false
• D. Statement (I) is false and Statement (II) is true

Answer 1

The correct option is B Both the statements are true and Statement II is not a correct explanation of Statement I

Given:
The order in which the energy of the available orbitals 4d, 5s and 5p increase is $5s<4d<5p$ .
Or we can say that, in the fifth period, 4f orbitals are not filled and 4d orbitals are fully filled as the last electron in the period goes to the 4d orbital.
For 4f orbital, $n+l$ = 7, so electrons will start to fill after 6s orbital
The number of elements in a period is equal to the number of electrons that can be accomodated in the available orbitals that are being filled for the given n.