<u>Answer:</u> The correct answer is Option D.
<u>Explanation:</u>
Atomic number is defined as the number of electrons or number of protons that are present in a neutral atom. It is represented as Z.
Z = Atomic number = Number of electrons = Number of protons
Mass number is defined as the sum of number of protons and number of neutrons present in an atom. It is represented as A.
A = Mass number = Number of protons + Number of neutrons
Number of neutrons = Mass number - Atomic number
For the given options:
Indium is the 49th element of the periodic table having mass number 115.
So, Number of protons = Number of electrons = 49
Number of neutrons = 115 - 49 = 66
Hence, this is not correctly described.
Scandium is the 21st element of the periodic table having mass number 45
So, Number of protons = Number of electrons = 21
Number of neutrons = 45 - 21 = 24
Hence, this is not correctly described.
Aluminium is the 13th element of the periodic table having mass number 27
So, Number of protons = Number of electrons = 13
Number of neutrons = 27 - 13 = 14
Hence, this is not correctly described.
Zinc is the 30th element of the periodic table.
So, Number of protons = Number of electrons = 30
This atom has 30 protons inside the nucleus and 30 electrons outside the nucleus.
Hence, this is correctly described.
Thus, the correct answer is Option D.