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Q:

An element which is preserved under water is 

A) sodium B) sulphur
C) red phosphorus D) white phosphorus
 
Answer & Explanation Answer: D) white phosphorus

Explanation:

White phosphorus undergoes spontaneous combustion when exposed to air. In order to prevent this spontaneous ignition, it is preserved under water. 

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Filed Under: Chemistry

Q:

Which of the following is called 'the King of Chemicals' ?

A) Nitric acid B) Hydrochloric acid
C) Silver nitrate D) Sulphuric acid
 
Answer & Explanation Answer: D) Sulphuric acid

Explanation:

Sulphuric acid is called the King of Chemicals because it is used in the preparation of a very large number of other useful chemicals such as hydrochloric acid, nitric acid, dyes, drugs etc. In fact the annual production of shulpuric acid in a country is a measure of the economy of the country.

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Filed Under: Chemistry

Q:

According to the modern Periodic Law, the properties of elements are periodic functions of their

A) volency B) atomic mass
C) number of neutrons D) atomic number
 
Answer & Explanation Answer: D) atomic number

Explanation:

Atomic number is the serial number of an element in the periodic classification of elements. It gives the number of protons and also the number of electrons in an atom.

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Filed Under: Chemistry

Q:

Washing soda is 

A) sodium hydroxide B) sodium carbonate
C) sodium bicorbonate D) Potassium chloride
 
Answer & Explanation Answer: B) sodium carbonate

Explanation:

Sodium hydroxide - NaOH is caustic soda

 

Sodium carbonate - Na2CO3 is washing soda

 

Sodium bicarbonate - NaHCO3  is baking soda 

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Filed Under: Chemistry
Exam Prep: AIEEE

Q:

A nuclear reactor is said to have become 'critical' when 

A) it stops due to malfunctioning B) it starts emitting dangerous radioactive radiations
C) it is shut down to avoid explosion D) it is ready to produce controlled energy
 
Answer & Explanation Answer: D) it is ready to produce controlled energy

Explanation:

To produce controlled energy i.e energy at a controlled or steady rate, the number of fissions per second must be controlled and maintained at that rate. Excess neutrons should be absorbed by control roads like cadmium.

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Filed Under: Physics

Q:

The electrical domestic tube light gives white fluorescent light because of

A) colision between molecules of filled gas under electric current B) heavy current
C) vacuum inside the tube D) falling of ultra violet rays on the white inner coating of the tube
 
Answer & Explanation Answer: D) falling of ultra violet rays on the white inner coating of the tube

Explanation:

The ultraviolet rays have high frequency and shorter wavelength are converted to visible white light with lower frequency and greater wave length

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Filed Under: Physics

Q:

Lightning is produced when 

A) Similar charges of electricity rush towards each other and then get repelled B) clouds strike against impurities in air and the friction burns up these impurities
C) strong opposite charges in different clouds break down the resistance offered by the intervening air D) water vapour produces electricity in the clouds
 
Answer & Explanation Answer: C) strong opposite charges in different clouds break down the resistance offered by the intervening air

Explanation:

When the resistance of the air between breaks down the current flows from the positive cloud to the negative cloud in a flash which we call lightning . The difference of potential involves is very high.

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Filed Under: Physics

Q:

The velocity required to place a vehicle in orbit round the moon is _______ that required to place it in orbit round the earth 

A) less than B) Greater than
C) equal to D) greater than or equal to
 
Answer & Explanation Answer: A) less than

Explanation:

This orbital velocity at the moon is less because orbital velocity = rg

 

where 'r ' is the orbital radius. i.e the distance of the body from the center of the earth and 'g' is the acceleration due to gravity on the body in question. In the case of the moon, both r and g are less than in the case of the earth.

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Filed Under: Physics
Exam Prep: AIEEE , GATE