**(a) **n = 4 (Given)

For some value of ‘n’, the values of ‘l’ range from 0 to (n – 1).

Here, the possible values of l are 0, 1, 2, and 3

Therefore, a total of 4 subshells are possible when n=4: the s, p, d and f subshells.

**(b)** No. orbitals in the n^{th} shell = n^{2}

For n = 4

Therefore, the total no. orbitals when n = 4 is 16

If each orbital fully occupied, each orbital will have 1 electron with m_{s} value of \( -\dfrac{1}{2}\).

Therefore, total no. electrons with an m_{s} value of \( (-\dfrac{1}{2})\) is 16.

Indicate the number of unpaired electrons in:

**(a)** P

**(b) **Si

**(c)** Cr

**(d)** Fe

**(e)** Kr

The unpaired electrons in Al and Si are present in 3p orbital. Which electrons will experience more effective nuclear charge from the nucleus?

Among the following pairs of orbitals which orbital will experience the larger effective nuclear charge?

**(i) **2s and 3s,

**(ii)** 4d and 4f,

**(iii)** 3d and 3p

The bromine atom possesses 35 electrons. It contains 6 electrons in 2p orbital, 6 electrons in 3p orbital and 5 electrons in 4p orbital. Which of these electron experiences the lowest effective nuclear charge?

The quantum numbers of six electrons are given below. Arrange them in order of increasing energies. If any of these combination(s) has/have the same energy lists:

**1.** n = 4, l = 2, \( m_l\) = –2 , ms = \( -\dfrac{1}{2}\)

**2.** n = 3, l = 2, \( m_l\)= 1 , ms = \( +\dfrac{1}{2}\)

**3.** n = 4, l = 1, \( m_l\) = 0 , ms = \( +\dfrac{1}{2}\)

**4.** n = 3, l = 2, \( m_l\)= –2 , ms = \( -\dfrac{1}{2}\)

**5.** n = 3, l = 1, \( m_l\) = –1 , ms= \( +\dfrac{1}{2}\)

**6.** n = 4, l = 1, \( m_l\) = 0 , ms = \( +\dfrac{1}{2}\)