Question

The number of electrons, neutrons and protons in a species are equal to 10, 8 and 8 respectively. The proper symbol of the species is:
A.$${}_8^{16}O$$
B.$${}_8^{18}O$$
C.$${}_{10}^{10}Ne$$
D.$${}_8^{16}{O}^{2-}$$

Answer 1

Hint: An element is represented by a general symbol $${}_z^{A}X$$ .
A represents the mass number.
Z represents the atomic number.
X represents the element.
Complete step by step answer:
An element is represented as X.
Every atom has a nucleus which has a positive charge. A nucleus has protons and neutrons, Protons are positively charged species and neutrons are chargeless species. These neutrons and protons are collectively called nucleons. Each nucleus will be surrounded by electrons. Electrons are negatively charged. The number of protons and electrons will be the same. Mass number is the sum of protons and neutrons. Difference between the mass number and atomic number will give the number of neutrons.
In O, the atomic number is 8. So, the number of protons and electrons are 8. Mass number is 16.
 So,16-8 =8. The number of neutrons will be 8.
In O, the atomic number is 8, so there will be 8 protons and 8 electrons. Mass number is 18. So, 18-8 =10
So, the number of neutrons will be 10.
In Ne, there will be 10 protons and electrons because the atomic number is 10. Mass number is 18. So, 18-10 =8. So, the number of neutrons will be 8.
In O, the atomic number is 8. The number of protons is 8. Due to the -2 charge we have to add two more electrons. The number of electrons will be 10. Mass number is 16. So, 16-8 =8. There will be 8 neutrons.
Hence the correct answer is D. O will have 10 electrons, 8 neutrons and 8 protons.

Note: Students should note that there are elements having the same atomic number and different mass number. These are known as isotopes. Example. Protium, Deuterium, tritium.
There are elements having the same mass number and different atomic number. These are known as isobars.
There are some elements having the same neutron number these are known as isotones.