Question

In which of the following cases block of the elements will change if $n+l$ rule is replaced by $n$ rule?

• A. $Li$
• B. $Na$
• C. $K$
• D. $Rb$

Answer 1

Answer: (C), (D)

The correct options are
C $K$
D $Rb$

a) $Li\left(3\right):1s^{2}2s^1\text{(s-block)}$

b) $Na\left(11\right):1s^{2}2s^{2}2p^{6}3s^1\text{(s-block)}$

c) $K\left(19\right):1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^1\text{(d-block)}$
$3d$ is being filled in the absence of $n+l$ rule.

d) $Rb\left(37\right):1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^{2}4p^{6}4d^1\text{(d-block)}$
$4d$ is being filled in the absence of $n+l$ rule.

$K$ and $Rb$ are s-block elements but in the absence of $n+l$ rule, they would be placed in d - block.