Chemistry Mock Test- 3 - Class 9 MCQ

 it  will be incorrect to say that  an  atom of  a compound   because, 
Every combination of atoms is a molecule. A compound is a molecule made of atoms  from different elements. All compounds are molecules , but not all molecules are compounds.

Dry ice, sometimes referred to as "cardice", is the solid form of carbon dioxide. It is used primarily as a cooling agent. Its advantages include lower temperature than that of water ice and not leaving any residue. 

Formula to change the value of celsius into kelvin is K = C + 273. As we know that boiling point of water is 100 c. SO, K = 100 + 273 K = 373 k.

Atomic mass of Magnesium is 12 and Sulphur is 16. Therefore, the ratio of Magnesium ans Sulphur by mass is 12:16 = 12/16 = 3:4.

Liquids will flow and fill up any shape of container. Solids like to hold their shape. In the same way that a large solid holds its shape, the atoms inside of a solid are not allowed to move around too much. Atoms and molecules in liquids and gases are bouncing and floating around, free to move where they want.

1. Starch solution

Explanation: A colloidal solution consists of tiny particles suspended in a continuous medium. The particle size in a colloid is between that of a true solution and a suspension, meaning the particles do not settle out upon standing.

• Starch solution is a colloid because the starch particles are small enough to remain suspended in water without settling.
• Copper sulphate solution is a true solution, not a colloid.
• Chalk powder in water is a suspension, as the chalk particles settle down when left undisturbed.
• Kerosene oil and water form an immiscible liquid mixture, not a colloid.

Thus, starch solution is the correct example of a colloidal solution.

Colloids

• Aluminium paint: Aluminium paint is a suspension, not a colloid. It consists of solid particles (aluminium) dispersed in a liquid medium (paint).


• Blood: Blood is a colloidal solution. It contains various proteins and cells suspended in plasma, which is the liquid component of blood.


• Milk: Milk is also a colloid. It is an emulsion of fat globules dispersed in water along with proteins and other components.


• All: The correct answer is "All" because both blood and milk are examples of colloids. Therefore, all the options given contain colloids.

In summary, while aluminium paint is not a colloid, both blood and milk are examples of colloids. Blood is a colloidal solution, and milk is an emulsion, making them both examples of colloids.

Matter is classified based on particle arrangement. The three main categories are solid, liquid, and gas, each characterized by different arrangements and behaviors of particles.

Water boils at 100ºC at atmospheric pressure. This is the temperature at which the liquid rapidly changes into a gas.

Option 2 illustrates the law of conservation of mass.

The law of conservation of mass states that in a chemical reaction, the total mass of the reactants is equal to the total mass of the products. This means that matter is neither created nor destroyed in a chemical reaction.

In option 2, 12 g of CO reacts with 32 g of O2 to form 44 g of CO2. The total mass of the reactants (12 g + 32 g = 44 g) is equal to the total mass of the product (44 g). This illustrates the law of conservation of mass.

Option 1 is an example of the law of definite proportions, which states that a given compound always contains the same elements in the same proportion by mass.

Option 3 is not a valid example of the law of conservation of mass, as heating carbon in a vacuum can lead to the release of gases such as carbon dioxide, carbon monoxide, and carbon suboxide, which can escape and change the mass of the system.

Option 4 is an example of a physical change, where the state of matter of a substance changes, but the mass of the substance remains the same. It does not illustrate the law of conservation of mass.

Carbon dioxide is a gas and has a weak intermolecular force of attraction between its molecules. It can be easily solidified and even liquified because it has a low melting point and low boiling point.

• KN0₃: Potassium nitrate has a solubility of 13.3 g/100 mL at 293 K.


• NaCl: Sodium chloride has a solubility of 35.7 g/100 mL at 293 K.


• KCl: Potassium chloride has a solubility of 34.0 g/100 mL at 293 K.


• NH₄Cl: Ammonium chloride has a solubility of 37.2 g/100 mL at 293 K.

Explanation:

Among the given options, NH₄Cl has the highest solubility at 293 K with a solubility of 37.2 g/100 mL. Therefore, NH₄Cl is the correct answer.

Air is a mixture of gases consisting of approximately 4/5 Nitrogen and 1/5 Oxygen.

Adding of common salt (NaCl) to water is physical change as no new substance is formed and no heat is evolved during addition of salt in water.

The mass number, also called atomic mass number or nucleon number, is the total number of protons and neutrons in an atomic nucleus. It is approximately equal to the atomic mass of the atom expressed in atomic mass units.

According to Dalton's Atomic Theory:
1. Atoms are indivisible:
- According to Dalton's theory, atoms are the smallest indivisible particles of matter.
- Atoms cannot be created, destroyed, or further divided into smaller particles.
2. Electrons, protons, and neutrons are found in atoms:
- While Dalton's theory did not specifically mention electrons, protons, and neutrons, it is now known that atoms are composed of these subatomic particles.
- Electrons are negatively charged particles that orbit the nucleus of an atom.
- Protons are positively charged particles found in the nucleus of an atom.
- Neutrons are neutral particles also found in the nucleus of an atom.
3. Atoms of various elements have the same properties:
- According to Dalton's theory, atoms of the same element are identical and have the same properties.
- Atoms of different elements have different properties.
- This concept is still valid, as different elements have unique atomic structures and properties.
4. Atoms are not destroyed in chemical reactions:
- According to Dalton's theory, atoms are rearranged during chemical reactions, but they are not destroyed or created.
- The total number of atoms before and after a chemical reaction remains the same.
- This principle is known as the law of conservation of mass.
In summary:
- Dalton's atomic theory proposed that atoms are indivisible and are composed of protons, neutrons, and electrons.
- Atoms of different elements have different properties, and atoms are not destroyed or created in chemical reactions.

Yes, homogenous mixture have a variable composition as the constituents are present in any ratio such as 1:2 or 1:3 etc

Explanation:

• Homogeneous vs. Heterogeneous: Homogeneous substances have uniform composition and properties throughout, while heterogeneous substances have non-uniform composition and properties.


• Stainless Steel (Option A): Stainless steel is a homogeneous mixture of iron, carbon, and other elements. It has a uniform composition and properties, so it is not heterogeneous.


• Brass (Option B): Brass is an alloy of copper and zinc, which forms a homogeneous mixture. It also has a uniform composition, making it not heterogeneous.


• Air (Option C): Air is a mixture of gases like nitrogen, oxygen, carbon dioxide, etc. It is a homogeneous mixture since the gases are evenly distributed throughout the air, making it not heterogeneous.


• Smoke (Option D): Smoke is a heterogeneous mixture of tiny solid particles and gases. It does not have a uniform composition or properties, making it heterogeneous.

Therefore, out of the given options, Smoke (Option D) is the heterogeneous substance.

An endothermic process is any process which requires or absorbs energy from its surroundings, usually in the form of heat. It may be a chemical process, such as dissolving ammonium nitrate in water, or a physical process, such as the melting of ice cubes. Insoluble heavy impurities involve the opposite of an endothermic process which is exothermic process one that absorbs energy in the form of heat.

Lead (Pb) is not a compound. It is an element present in its pure form so it is a single homogeneous identity. Compounds have two or more elements present in the uniform composition in the compound state.

Explanation:

• Particles of suspension: Suspensions are heterogeneous mixtures in which particles are dispersed in a medium but are too large to stay permanently suspended. These particles can be seen with the naked eye.


• Visibility: Unlike solutions, where the particles are very small and cannot be seen with the naked eye, particles in a suspension are large enough to be visible.


• Settling: Suspensions tend to settle over time due to the force of gravity acting on the particles. This settling is visible and is one of the characteristics of a suspension.


• Examples: Common examples of suspensions include muddy water, chalk-water mixture, and some types of paint.

B is the correct option.
1.Aerosol particles originating from urban and industrial pollution or smoke from fires have been shown to affect cloud microphysics, cloud reflection of sunlight to space, and the onset of precipitation.
2. a fine dispersion of minute droplets of one liquid in another in which it is not soluble or miscible.
3.Whipped cream is an air-in-water foam in which air cells are surrounded by a film containing fat droplets stabilized by a film of protein. 
4. The use of sol-silicate paint protects the old substrate from further destruction due to UV exposure, and creates an absolutely lightfast and colour-stable surface. 

Let the relative abundance% of Ne -20 = x1
So, relative abundance% of Ne -22 =  x2

Now, we know that atomic mass = sum of relative abundance in atomic mass of each isotope / 100% 

20.2 = 20 x1 + 22 x2 / x1 +x2 
20.2 x1 + 20.2x2 = 20x1 + 22x2
0.2x1 =  1.8 x2 

x1 / x2  = 1.8/ 0.2 = 9/1   ( relative abundance) 

x1%  =  9/10 * 100  = 90%  lighter isotopes
x2%  =  1/ 10* 100  = 10%   heavier isotope 

The atomic number is the number of electrons present in an atom. We know that an atom has the same number of electrons & Protons. Therefore Chlorine is the element that has 17 protons. Hence the element is Chlorine.

Detailed

• Element Symbol Formation: The symbol of an element is represented by the element's atomic number (Z) as the subscript and the element's mass number (A) as the superscript.


• Given Information: Element X has a mass number of A and an atomic number of Z.


• Correct Symbol Formation: The correct symbol formation for element X based on the given information is ^A_ZX.


• Options Analysis:
  
  
  
  • Option A: _AX^Z
  
  
  • Option B: ^A_ZX (Correct Answer)
  
  
  • Option C: ^Z_AX
  
  
  • Option D: ^ZX_A
  
  
  
  


• Conclusion: Therefore, the correct symbol of element X with mass number A and atomic number Z is represented as ^A_ZX, which corresponds to Option B.

The correct answer is D: Both A and B.

- Precipitation Reaction: AgNO3(aq) + KCl(aq) → AgCl(s) + KNO3(aq) forms a solid precipitate.
- Double Displacement Reaction: AgNO3(aq) + KCl(aq) → AgCl(s) + KNO3(aq) involves the exchange of ions between two compounds.
- Explanation: The given reaction demonstrates both characteristics, forming a precipitate (A) and involving double displacement of ions (B), making it both a precipitation and a double displacement reaction.

The ground state electron configuration of ground state gaseous neutral phosphorus is [Ne]. 3s².3p³