276. Assertion (A) : Out in space, the sky looks dark and black, instead of blue.
     Reason (R) : There is no atmosphere.

1. 1. If (A) and (R) are correct and (R) is the correct explanation of (A)

   
   
   

   2. If (A) and (R) are correct but (R) is not the correct explanation of (A)

   
   
   

   3. If (A) is true but (R) is false

   
   
   

   4. If (A) is false but (R) is true

   
   
   

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   NA

   Correct Option: A

   NA

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277. Which of the following pair is wrongly matched

1. 1. Mesosphere - Extends out to about 100 km

   
   
   

   2. Thermosphere - Extends out to about 400 km

   
   
   

   3. Exosphere - Extends beyond the Thermosphere hundreds of kilometers

   
   
   

   4. Stratosphere - Extends out to about 500 km

   
   
   

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   NA

   Correct Option: D

   NA

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278. A layer in the Earth s atmosphere called Ionosphere facilitates radio communication Why ?
     1. The presence of ozone 'causes the, reflection of radio waves to Earth.
     2. Radio waves have a very long wavelength.
     Which of the statements given above is / are correct

1. 1. 1 only

   
   
   

   2. 2 only

   
   
   

   3. Both 1 and 2

   
   
   

   4. Neither 1 nor 2

   
   
   

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   NA

   Correct Option: D

   NA

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279. Assertion (A) : The warmer portions of the water are less dense and therefore, they rise.
     Reason (R): The cooler portions of the water fall because they are denser.

1. 1. If (A) and (R) are correct and (R) is the correct explanation of (A)

   
   
   

   2. If (A) and (R) are correct but (R) is not the correct explanation of (A)

   
   
   

   3. If (A) is true but (R) is false

   
   
   

   4. If (A) is false but (R) is true

   
   
   

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   NA

   Correct Option: B

   NA

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280. Assertion (A) : The blue colour of the sky is due to Ray light scattering.
     Reason (R) : As light moves through the atmosphere, most of the longer wavelengths pass straight through.

1. 1. If (A) and (R) are correct and (R) is the correct explanation of (A)

   
   
   

   2. If (A) and (R) are correct but (R) is not correct explanation of (A)

   
   
   

   3. If (A) is true but (R) is false

   
   
   

   4. If (A) is false but (R) is true

   
   
   

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   NA

   Correct Option: B

   NA

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