451. The cooling by a desert cooler is based on-

1. Hot air replacement
2. Air dehydration
3. Evaporative cooling
4. Air rehydration

Option “3” is correct.
The cooling by a desert cooler is based on evaporative cooling. These coolers are also known as swamp coolers.
452. Cooling by air conditioner is done by-

1. Flow of water
2. Release of compressed gas
3. Cooking gas
4. Melting the solid

Option “2” is correct.
Most of the air conditioner uses compressed gas, which can cool the room or other places.
453. On adding common salt to water, the boiling point and freezing point of water will:

1. Increase
2. Decrease
3. Decrease and increase respectively
4. Increase and decrease respectively

Option “4” is correct.
If salt is added to the water then the boiling point of water will increases. This happens as the boiling point is the temperature at which the vapor pressure of solvent becomes equal to the external atmospheric pressure. Similarly it also decreases the freezing point, which in turn will interfere with the frozen solution’s crystal structure. That means the temperature will have to be colder to overcome it and freeze the mixture anyway.
454. Good conductor of electricity is –

1. Dry air
2. Paper
3. Kerosene
4. Graphite

Option “4” is correct.
Graphite is soft and slippery because there are only weak inter molecular forces between its layers. Graphite is a good conductor of heat and electricity.
455. Fish can survive in a frozen lake because-

1. Fish are warm blooded animals
2. Fish hibernate in ice
3. Water near the bottom does not freeze
4. Ice is a good conductor of heat

Option “3” is correct.
This is because of a phenomenon is known as winter stratification in water bodies. In the winter season, the water at the top layer of water bodies will be ice cold (0°C) and are gradually frozen. But still, the bottom layers will have liquid water and maintain a temperature (4°C) which supports the life there. Thus, fishes and other aquatic animals are saved from the frozen top layer of water.
456. The colour of light is determined by its-

1. Amplitude
2. Wavelength
3. Intensity
4. Velocity

Option “2” is correct.
The color of light is determined by its wavelength. Different colors have different wavelengths. The wavelength of red colour is largest and violet colour has shortest wavelength.
457. Which one of the following is used as a moderator in the nuclear reactor?

1. Thorium
2. Graphite
3. Radium
4. Ordinary water

Option “2” is correct.
Many of the nuclear reactors use graphite as a moderator. Graphite is not as effective as heavy water, but it is cheaper and it also has a low degree of neutron capture like heavy water.
458. At what temperature (in degree Celsius), the numerical values on Celsius and Fahrenheit scales become equal?

1. –40
2. 40
3. 273
4. –273

Option “1” is correct.
At -40 degrees, the numerical values on Celsius and Fahrenheit scales become equal.
459. What is the process of conversion of solid state directly to gaseous state called?

1. Evaporation
2. Condensation
3. Sublimation
4. Distillation

Option “3” is correct.
Sublimation is the phase transition of a substance directly from the solid to the without passing through the intermediate liquid phase.
460. When a ball is thrown vertically upwards, which of the following quantities remains constant during its motion?

1. Acceleration due to gravity
2. Displacement
3. Velocity
4. None of these

Option “1” is correct.
When a ball is thrown vertically upwards Acceleration due to gravity remains constant during its motion.
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