Question

The Z and A values of an element are 25 and 55. The number of electrons, protons, and neutrons in its most stable ion respectively are
A.25,25, 30
B. 23, 25, 30
C.22, 25, 30
D.20, 25, 30

Answer 1

Hint: We know that, an element is represented in the form of ${}_{\rm{Z}}^{\rm{A}}{\rm{X}}$. Here, X is the particular element, A is the element's mass number and Z is the atomic number of the element. The Z (atomic number) value of an element gives the count of protons in the element.

Complete step by step answer:
We know that, summation of number of protons and neutrons of an element gives its mass number.

Now come to the question. The atomic number (Z) of the element is 25 and the mass number (A) is given as 55.

So, from the above information we get to know that the number of protons in the element is 25.

Now, we have to calculate the number of neutrons using the formula of mass number, that is,

Mass number=Number of protons + Number of neutrons

For the element,

Number of neutrons=Mass number- Number of protons
$ \Rightarrow $Number of neutrons=55-25=30

To determine the most stable ion of the element, first we have to write the electronic configuration of the element. Half-filled electrons orbitals are most stable. So, the electronic configuration of the element (atomic no -25) is,

$1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}4{s^2}3{p^5}$


So, if two outermost electrons are donated by the element, the formed ion will be the most stable ion as p–orbital then become half filled and we know that half filled orbitals are most stable. So, the number of electrons in the most stable ion is 23.

number of electrons=23, number of protons=25 and number of neutrons=30

So, the correct answer is Option B .

Note:
Always remember that, there are three subatomic particles namely, neutron, proton and electron. Electrons possess negative charge, proton possesses positive charge and neutron bears no charge. Nucleus is the centre of the atoms and electrons are rotating around the nucleus.