Question

The position of an atom with $Z=24$ in the periodic table is in:
(A) V A group and 4th period
(B) I A group and 4th period
(C) IV A group and 3rd period
(D) III B group and 3rd period

Answer 1

Hint :In order to answer this question, first we will write the electronic configuration of the element of atomic number 24. And then we will check whether the valence electrons are entering which shell, and that shell indicates the period, and the outer electronic configuration indicates the group.

Complete Step By Step Answer:
Atom with $Z=24$ has the electronic configuration:
$$\begin{array}{l}1s^2,2s^2,2p^6,3s^2,3p^6,3d^5,4s^1\end{array}$$
The valence electron enters the 4th shell $(4s^1)$ according to the electrical arrangement, putting the element in the fourth period.
Since the outer electronic configuration of the element is $(4s^1)$ it belongs to IA group or alkali-metals.
Therefore, the element with $Z=24$ belongs to I A group and the 4th period.
Hence, the correct option is (B) I A group and 4th period.

Note :
Atomic number 24 is Chromium. On the periodic table, chromium is the fourth transition metal, with an electron configuration of $$\left[Ar\right]\text{ 3}{d}^{5}4s^1$$ . It's also the first element in the periodic table to defy the Aufbau principle in its ground-state electron structure. Other elements and their electron configurations, such as copper, niobium, and molybdenum, appear later in the periodic table.