Chapter 3, Problem 1TQ

Summary Introduction

All materials are made from atoms. More than hundred different types of atom that has chemical and physical properties are called an element. An atom is the smallest unit of an element with distinctive properties. Every atom is made up of a nucleus consisting of neutrons (neutral charge) and protons (positive charge), and negatively charged electrons that surrounds the nucleus.

Answer to Problem 1TQ

The number of protons in the atom determines the atomic number of an atom.

Therefore, option (a) is correct. 

Explanation of Solution

Justify the reasons for the correct statement:

The number of protons in an atom’s nucleus is referred to as the atomic number. The atomic number of an atom is denoted by the symbol “Z”.

Option (a) is given as “protons”.

Hence, the option (a) is correct.

Justify the reasons for the incorrect statements:

Option (b) is given as “neutrons”.   

Neutrons determines the neutrally charged particles in an atom. It does not determines the atomic number of an atom. Hence, it is a wrong answer.

Option (c) is given as “electrons”.

Electrons are negatively charged particles that surrounds the nucleus of an atom. The number of electrons does not determine the atomic number. Hence, it is a wrong answer.

Option (d) is given as, “electrons plus neutrons plus protons”.   

Electrons plus neutrons plus protons constitutes an atom, and it does not determine the atomic number. Hence, it is a wrong answer.

Hence, options (b), (c), and (d) are incorrect.

Conclusion

Atomic number of an atom is determined by the number of protons in the atom.