Chemistry 9th Chap 3 : Topic 8 - Maryam Publications

Chemistry Chapter 3 : Topic 8

Atomic Number and Periodic Table

1 / 10

An element is defined scientifically by the number of protons present in the nucleus of its atom. This number remains unchanged even if the atom gains or loses electrons or neutrons. Which conclusion correctly explains why proton number is considered the identity of an element?

A) Because it can change during chemical reactions

B) Because it equals the mass number of all atoms of that element

C) Because it uniquely identifies an element regardless of isotopes or ions

D) Because it determines the physical state of the element at room temperature

2 / 10

Two atoms are given: Atom A has 6 protons and Atom B has 7 protons. Both atoms are neutral. Which statement best explains their relationship in terms of periodic table classification?

A) They belong to different elements due to different proton numbers

B) They differ only in number of electrons, not in element type

C) They have identical chemical properties because both are neutral

D) They are isotopes of the same element

3 / 10

In the modern periodic table, elements are arranged in order of increasing atomic number rather than atomic mass. What is the main scientific reason for this arrangement?

A) Proton number determines chemical properties more consistently than mass

B) Atomic number changes during chemical reactions

C) Neutrons have no role in atomic structure

D) Atomic mass is always inaccurate for elements

4 / 10

An atom loses one electron and becomes positively charged. Despite this change, it remains the same element. What is the reason behind this?

A) Because neutron number increases automatically

B) Because proton number remains unchanged

C) Because mass number becomes zero

D) Because electrons determine the element’s identity

5 / 10

Three atoms are observed:

A) They are different elements due to different neutrons

B) They are isotopes of the same element

C) They belong to different groups in periodic table

D) They are ions of different elements

6 / 10

A student states: “If two atoms have the same number of neutrons, they must be the same element.” Why is this statement incorrect?

A) Because neutrons are not present in atoms

B) Because proton number, not neutron number, defines the element

C) Because electrons are always equal in all atoms

D) Because neutrons determine chemical reactivity

7 / 10

The periodic table was developed based on a fundamental property of atoms that increases step by step across elements. Which property is this?

A) Number of neutrons

B) Proton number (atomic number)

C) Number of electrons in outer shell only

D) Atomic mass only

8 / 10

An unknown element has atomic number 12. Another element has atomic number 13. Even if both show similar metallic properties, they are placed separately in the periodic table. What is the main reason?

A) Their neutron numbers are identical

B) Their masses are equal

C) Their electrons are the same

D) Their proton numbers are different

9 / 10

Which statement best explains why no two different elements can have the same proton number?

A) Because atomic mass is always unique

B) Because proton number is fixed and defines nuclear identity

C) Because electrons always define elements uniquely

D) Because neutrons prevent overlap of elements

10 / 10

A researcher modifies an atom by increasing its neutron number while keeping proton number constant. What change will occur in the periodic table position of this atom?

A) It will become a different element

B) It will remain in the same position as the same element

C) It will disappear from the periodic table

D) It will move to a different group

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