Structure Of The Atom, Science, Class 9 - Test - Class 9 MCQ

The nucleons are:
- Protons: Protons are positively charged subatomic particles found in the nucleus of an atom. They have a mass of approximately 1 atomic mass unit (u) and a charge of +1.
- Neutrons: Neutrons are neutral subatomic particles found in the nucleus of an atom. They have a mass of approximately 1 atomic mass unit (u) but no charge.
- Electrons: Electrons are negatively charged subatomic particles that orbit around the nucleus of an atom in electron shells. They have a very small mass compared to protons and neutrons.
- Nucleus: The nucleus is the central part of an atom that contains the nucleons. It is composed of protons and neutrons tightly bound together.
- Nucleons: Nucleons refer to both protons and neutrons collectively. They are the subatomic particles found in the nucleus.
- Answer: The correct answer is C. Protons and neutrons are the nucleons found in the atomic nucleus.

Isotope Deuterium of Hydrogen
Facts about Deuterium:
- Deuterium is an isotope of hydrogen.
- It is represented by the symbol D or ²H.
- It is a stable isotope, meaning it does not undergo radioactive decay.
Composition of Deuterium:
- Deuterium has one proton and one neutron in its nucleus.
- It does not have any electrons in its nucleus.
Comparison to Regular Hydrogen:
- Regular hydrogen, also known as protium, has only one proton and no neutrons.
- The most common isotope of hydrogen is protium, which is the simplest and lightest element.
Answer:
- The isotope deuterium of hydrogen has one proton and one neutron in its nucleus.
- Therefore, the correct answer is option D: one proton and one neutron.

Valence Electrons
Valence electrons are the electrons that are present in the outermost shell or energy level of an atom. They are responsible for the chemical properties of an element and play a crucial role in the formation of chemical bonds.
Key Points:
- The outermost shell of an atom is also known as the valence shell.
- Valence electrons determine the number of bonds an atom can form with other atoms to achieve a stable electron configuration.
- The number of valence electrons can be determined by the group number of the element in the periodic table.
- Elements in the same group have the same number of valence electrons.
- Valence electrons are important in predicting the reactivity and chemical behavior of elements.
- The noble gases have a full outermost shell with eight valence electrons, except for helium, which has two.
- Valence electrons can be represented using Lewis dot symbols, where each dot represents one valence electron.
In conclusion, the electrons present in the outermost shell of an atom are called valence electrons. They are crucial in determining the chemical properties and reactivity of elements.

Explanation:
- An α-particle is a type of particle that is emitted during certain types of radioactive decay.
- It consists of two protons and two neutrons, which means it has a total charge of +2 (since protons have a positive charge) and a total mass of 4 atomic mass units (since protons and neutrons both have a mass of approximately 1 atomic mass unit).
- The correct option is B because it states that an α-particle contains 2 positive charges and 4 mass units, which matches the composition of an α-particle.
- Option A is incorrect because it states that an α-particle contains 4 positive charges, which is twice the actual charge of an α-particle.
- Option C is incorrect because it states that an α-particle contains 2 positive charges and 2 mass units, which is half the actual mass of an α-particle.
- Option D is incorrect because it states that an α-particle contains 4 positive charges and 4 mass units, which is double the actual mass of an α-particle.

The atomic number of an element represents the number of protons in its nucleus, while the mass number represents the total number of protons and neutrons.
In the case of sodium:
- Atomic number = 11, which means it has 11 protons.
- Mass number = 23, which means it has a total of 23 protons and neutrons.
To determine the number of neutrons and electrons in sodium, we can use the following formulas:
- Number of neutrons = Mass number - Atomic number
- Number of electrons = Atomic number
Using the formulas:
- Number of neutrons = 23 - 11 = 12
- Number of electrons = 11
Therefore, the correct answer is:

C:

11 electrons and 12 neutrons

The electronic configuration of chlorine is 2, 8, 7.
Explanation:
- The atomic number of chlorine is 17, which means it has 17 electrons.
- The electronic configuration is a representation of how these electrons are distributed in different energy levels or shells around the nucleus.
- The first energy level can hold a maximum of 2 electrons, the second energy level can hold a maximum of 8 electrons, and the third energy level can hold a maximum of 8 electrons as well.
- Starting from the innermost energy level, we distribute the electrons into the available slots until we have accounted for all of them.
- In the case of chlorine, we first fill the first energy level with 2 electrons.
- Then, we move on to the second energy level and fill it with 8 electrons.
- Finally, we place the remaining 7 electrons in the third energy level.
- Therefore, the electronic configuration of chlorine is 2, 8, 7.
So, the correct answer is option C: 2, 8, 7.

The isotope used to remove brain tumors and treat cancer is Co-60.
Explanation:

• What are isotopes?




• Isotopes are atoms of the same element that have different numbers of neutrons in their nuclei.


• Isotopes of an element have the same atomic number but different mass numbers.




• Co-60 (Cobalt-60)




• Co-60 is an isotope of the element cobalt.


• It is a radioactive isotope with a half-life of about 5.27 years.


• Co-60 is used in medicine for radiation therapy in the treatment of cancer.


• It emits gamma rays, which can penetrate tissues and destroy cancer cells.


• Co-60 can be used for external beam radiation therapy or for internal radiation therapy (brachytherapy).




• Other options:




• A: U-235 (Uranium-235) is used as fuel in nuclear reactors and for the production of nuclear weapons.


• B: Na-24 (Sodium-24) is used in research and medical imaging techniques.


• C: Iodine is used in nuclear medicine for imaging thyroid disorders.

Therefore, the correct answer is d. Co-60 (Cobalt-60).

Explanation:
In order to identify the isobars, we need to compare the pressure patterns shown in the given diagrams. Isobars are lines that connect points of equal atmospheric pressure.
Let's analyze each option:
Option A:
- In the first diagram, the isobars are evenly spaced and concentric circles, indicating a high-pressure system.
- In the second diagram, the isobars are also evenly spaced and concentric circles, indicating a low-pressure system.
- The pressure patterns in the two diagrams are different, so option A does not show isobars.
Option B:
- In the first diagram, the isobars are evenly spaced and form closed curves, indicating a high-pressure system.
- In the second diagram, the isobars are also evenly spaced and form closed curves, indicating a low-pressure system.
- The pressure patterns in the two diagrams are similar, so option B shows isobars.
Option C:
- The diagram shows a single closed curve, which does not represent isobars.
- Option C does not show isobars.
Option D:
- The diagram shows a single closed curve, which does not represent isobars.
- Option D does not show isobars.
Therefore, the correct answer is option B, which shows isobars.

Valence Electrons and Ion Formation
To determine which elements have the same valence electrons and form the same type of ions, we need to analyze the given images and their corresponding electron configurations.
A: Image 1
- The electron configuration for this image is 2, 8, 8, 2.
- The elements in this image belong to Group 2, which is the alkaline earth metals.
- Alkaline earth metals have 2 valence electrons and tend to lose them to form a +2 ion.
B: Image 2
- The electron configuration for this image is 2, 8, 7.
- The elements in this image belong to Group 17, which is the halogens.
- Halogens have 7 valence electrons and tend to gain one electron to form a -1 ion.
C: Image 3
- The electron configuration for this image is 2, 8, 6.
- The elements in this image belong to Group 16, which is the chalcogens.
- Chalcogens have 6 valence electrons and tend to gain two electrons to form a -2 ion.
D: Image 4
- The electron configuration for this image is 2, 10, 2.
- The elements in this image belong to Group 2, which is the alkaline earth metals (same as Image A).
- Alkaline earth metals have 2 valence electrons and tend to lose them to form a +2 ion.
Conclusion:
From the given images, we can determine that:
- Image A and Image D represent elements with the same valence electrons (2) and form the same type of ions (+2).
- Image B represents elements with 7 valence electrons and form a -1 ion.
- Image C represents elements with 6 valence electrons and form a -2 ion.
Therefore, the answer is d. Image D represents elements with the same valence electrons and form the same type of ions.

In the α-scattering experiment, few α-particles rebounded because positive charge of the atom occupies very little space.