Question

An element M has an atomic number 9 and atomic mass 19. Its negative ion will be represented by:
(A) M
(B) ${{M}^{2+}}$
(C) ${{M}^{-}}$
(D) ${{M}^{2-}}$

Answer 1

Hint: Atoms are composed of neutrons, protons, and electrons, the basic building blocks of all matter. Atoms are electrically neutral because of the number of positively charged protons equal to the number of negatively charged electrons. Since neutrons are not charged and do not depend on the atomic number of atoms.

Complete step by step solution:
The given atomic number of element M =9
The mass number of the element M =19
When element forms ion due to the removal of electrons or adding of an electron from the valence shell, resulting in the formation of positive ions or negative ions respectively. The positive ion is known as cation when the electron is removed from an element and the negative ion is known as anion when an electron is added to an element.
The atomic number is defined as the number of electrons or protons present in an element and mass number is defined as the number of protons and neutrons present in the nucleus of an element.
Number of electrons present in the given element M =9 because atomic number Z=9
The electronic configuration of element M =$1{{s}^{2}}2{{s}^{2}}2{{p}^{5}}$
This element requires one electron to get the noble gas configuration of neon. So, the element easily accept one electron and become a negative ion with a -1 charge
Thus, the ion of an element having atomic number 9 is ${{M}^{-}}$

The correct answer is option C.


Note: The atomic number of elements depends on the number of protons or the number of electrons in the element but not depend on the number of neutrons. So, the electron count will equal the number of protons. The atomic mass number of an element depends on the number of protons, neutrons, and electrons.