Question

A neutral atom of an element has 2K, 8L and 5M electrons. Atomic number of neutral atom is:
A.$20$
B.$18$
C.$15$
D.$25$

Answer 1

Hint:In the given question firstly we have to get the number of the total electrons that are in the given set of neutral atom as that would give us the number of the protons for the atom, which for this case would sum up to $15$ . Now after this we know that the atomic number would be exactly equal to the number of protons in the neutral atom.

Complete step by step answer:
Here according to the question statement we get that the supposed atom in the problem have subsequent number of atoms in each of the shells of its given shells :
i.In the $K$ shell : $2$
ii.In the $L$ shell : $8$
iii.In the $M$ shell : $5$
Now this signifies that the given number of electrons in the given atom would add up to the $15$ and in the problem statement we know that the element is neutral so there would be an equal number of the protons in the given set of the atom.
We can say that as for the case of a neutral atom in its native state:
 Number of protons = number of electrons
So by this we know that the number of the protons would be $15$ , and therefore the atomic number signifies the number of the proton in the atom.
This all accounts to the atomic number being $15$ .
Hence the electronic configuration would be as per the subshells :
$1{s^2}2{s^2}2{p^6}3{s^2}3{p^1}$
So the right option would be option C, $15$ .

Note:
The atomic number or proton number (symbol Z) of a chemical element is the number of protons found in the nucleus of every atom of that element. The atomic number uniquely identifies a chemical element. It is identical to the charge number of the nucleus.