Chapter 2, Problem 1A

Summary Introduction

Introduction:

Atoms are called as the smallest unit of an element, which retains its physical as well as the chemical properties of the element. It is the smallest unit that can enter into any chemical reaction, although it can be split. Atoms possess an atomic symbol as well as an atomic number

Answer to Problem 1A

Correct answer:

The atomic number provides the number of protons in a nucleus. Therefore, option (b) is correct

Explanation of Solution

Reasons for the correct statement:

In an element, all the atoms of the nucleus possess same number of the protons. This is known as the atomic number. Thus, this forms the unique property of a particular element

Option (b) is given as “number of protons in the nucleus”

“The atomic number gives the number of protons in the nucleus”, it is the right answer”

Hence, option (b) is correct

Reasons for the incorrect statements:

Option (a) is given as “number of neutrons in the nucleus”.
Atomic number is not the number of neutrons in the nucleus; instead it consists of the number of protons. So, it is a wrong answer

Option (c) is given as “weight of the atom”.
Weight of an atom is based on the number of atoms or number of particles that are present in 1 mole of an atom. It does not mean the atomic number. So, it is a wrong answer

Option (d) is given as “number of protons in the valence shell”.
The valence shell of an atom comprises of electrons. It does not mean the atomic number. So, it is a wrong answer

Hence, options (a), (c) and (d) are incorrect

Conclusion

The atomic number provides the number of protons in a nucleus