Question

Ten elements in the periodic table resemble the ……………………… .
(A) First period
(b) second period
(c) fourth period
(d) ninth period

Answer 1

Cellulose is the main chemical that forms the important structure of plants; it is the most abundantly found organic macromolecule on Earth. Cellulose is extremely rigid that gives great strength to the plant body; it protects the inner parts of plant cells.
There are $2\ \text{to}\ 7$ monomens in a cellulose $\beta$-glucose the monomer unit of cellulose.

Complete step by step answer:
The electronic configuration of the tenth element in the periodic table will be:
$10=1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}$
This means that we are actually referring to the element’s atomic number. Hence, we have to find out the period to which the element having atomic number $10$ belongs to. The number of electrons in any element is equal to its atomic number. Hence, this element has a total of $10$ electrons. We will now try to devise the electronic configuration of this element by using the Aufbau principle. As we know, the first orbital in any electronic configuration is $1s$ , which can hold a total of $2$ electrons. The next is $2s$, which can also hold $2$ electrons. Next comes $2p$, which can hold a total of six electrons. As we can see, from these first three orbitals itself fill up our element’s $10$ electrons and there are no more electrons to be added.
The period is two because; the last electron of the outermost shell has the principal quantum number which is two. The principal quantum number n is two and hence the period is two. It is a block element so the valence electrons are added with the entire electron.
Group number $=10+$ valence electrons
$=18$

Hence, the correct option is B.

Additional Information:
The highest shell, or the valence shell, also denotes the element’s principal quantum number, denoted by $n$. The Aufbau principle states that electrons are filled into atomic orbital’s in the increasing order of orbital energy level. That is, $1s$ is filled before $2s$, which is filled before $2p$ and so on. Note that we can also approach this question like this: We know the first shell can accommodate $2$ electrons and the second shell can accommodate a total of $8$ electrons. Therefore, the total of $10$ electrons are filled in the first two shells, and hence, as the period number is equal to the total number of shells, this element belongs to the second period.

Note: Electronic configuration is used for:
Determining the valency.
Finding the properties of the group of elements.
Explaining the atomic spectra.