Question

List-I	LIST-II
(P) Mass number	1) A
(Q) Atomic number	2) A - Z
(R) No. of neutrons	3) K
(S) 2 electrons	4) Z

A. P-1, Q-2, R-3, S-4
B. P-1, Q- 4, R-2, S-3
C. P-2, Q-1, R-3, S-4
D. P-4, Q-1, R-2, S-3

Answer 1

. As we know that protons are positively charged, electrons are negatively charged. If we have to find the number of neutrons, we will subtract the atomic number from the mass number. And we can easily find the electrons, neutrons and protons.

Complete step by step answer:
- As we all know that atomic number is denoted by the symbol (Z), which denotes the total number of protons present in the nucleus of an atom. Let us consider an example, the mass number of aluminium is 27, and we know that the atomic number of aluminium is 13.
- It is found that the number of protons is equal to the atomic number. This clearly means that any atom which is an isotope of aluminium will basically have 13 protons in the nucleus.
- And the number of electrons is equal to the proton number. Hence, we can say that there will be 13 electrons.
- Now, we will calculate the number of neutrons present. As we know that mass number is denoted by the symbol (A) = number of protons + number of neutrons. Hence, the number of neutrons will be = 27 - 13 = 14. Or we can say that the number of neutrons is equal to mass number(A) - atomic number(Z).
As we know that the shell value is denoted by the principal quantum number (n). K = 1, L = 2, M = 3, N = 4, O = 5. It gives us the idea of how many electrons are present in the shell.
- It was observed that, K shell contains 2 total electrons, L shell contains 8 total electrons, M shell contains 8 total electrons, N shell contains 16 total electrons.
- From the above discussion we can conclude that the correct option is (B), that is P-1, Q- 4, R-2, S-3
So, the correct answer is “Option B”.

Note: - We should note that the total number of neutrons present in the nucleus is equal to the difference between the atomic number and the mass number of an atom.
- As we know that the mass number of any atom is basically equal to the addition of the protons and neutrons that are present in the nucleus.