Matter In Our Surroundings, Science, Class 9 - Test - Class 9 MCQ

Under low-pressure condition, we can boil water at room temperature. Explanation: When we heat the water, the temperature of the water rises. Due to this the water molecule “gains kinetic energy” and starts to move and escapes to the atmosphere in the form of vapor.

Condensation is the process in which any substance change into liquid from its gaseous form. Eg- Water changes from its gaseous form by the process of condensation.

Fusion is the process that powers the sun and the stars. It is the reaction in which two atoms of hydrogen combine together, or fuse, to form an atom of helium. In the process some of the mass of the hydrogen is converted into energy.

 

Ice floats on water because it is less dense than water.

When water freezes into its solid form, its molecules are able to form more stable hydrogen bonds locking them into positions. Because the molecules are not moving, they're not able to form as many hydrogen bonds with other water molecules. This leads to ice water molecules not being as close together as in the case of liquid water, thus reducing its density.

Most substances in their solid form are more dense than their liquid forms. The opposite is true in water. This property of water is somewhat unusual and rare.

Water is actually most dense at 4ºC. At any temperature below or above 4ºC, water becomes less dense.

Ice is in solid state while water is in liquid state. Thus, ice will convert into liquid state by absorbing the latent heat of fusion. On the other hand, no such heat will  be absorbed by water as it is already in the liquid state. Hence, ice will absorb more energy than water at 273K or 0^o C. The more is the energy absorbed, the more is the cooling effect. As a result, the cooling effect of ice at 273 K or 0^o C is more than water at the same temperature. 

The correct answer is C: Temperature.
Explanation:
Endothermic processes are those that absorb heat from their surroundings. They typically involve a change in state or the breaking of bonds, which requires an input of energy. Let's examine each option to determine which one is not an endothermic process:
A: Fusion
- Fusion refers to the process of melting a solid substance into a liquid state.
- This process requires an input of energy to break the intermolecular forces holding the solid together.
- Therefore, fusion is an endothermic process.
B: Vaporization
- Vaporization, also known as evaporation, is the process of converting a liquid into a gas.
- This process requires an input of energy to overcome the intermolecular forces holding the liquid together.
- Therefore, vaporization is an endothermic process.
C: Temperature
- Temperature is not a process but a measure of the average kinetic energy of particles in a substance.
- It is not an endothermic process as it does not involve a change in state or the breaking of bonds.
- Therefore, temperature is not an endothermic process.
D: Evaporation
- Evaporation, similar to vaporization, is the process of converting a liquid into a gas.
- It requires an input of energy to overcome the intermolecular forces holding the liquid together.
- Therefore, evaporation is an endothermic process.
In conclusion, temperature is not an endothermic process.

Gases can dissolve in water.

The dissolving of a gas in water depends on the interaction between the molecules of the gas and the water molecules.

The amount of gas that can be dissolved in water depends on the temperature of the water.

More gas can dissolve in cold water than in hot water.

By heating a gas, the volume of gas will expand because molecule of that gas will get kinetic energy through heating.

When atmospheric pressure is decrease, the boiling point of water will also decrease because boiling point is the temperature at which the vapour pressure of a liquid becomes equal to that of the atmosphere. If the atmospheric pressure decreases, then the vapour pressure of the liquid will also have to be decreased, for which the liquid has to be cooled down. Hence the boiling point of a liquid decreases.

Water is the only substance here which can exist in vapour state.