20
Q:

What kind of crystalline solid is graphite?

A) Metallic B) Ionic
C) Molecular D) Covalent- network

Answer:   D) Covalent- network



Explanation:

Graphite is a covalent-network type of crystalline solid.

 

There are two main categories of solids.

1. Crystalline solids and

2. Amorphous solids.

Crystalline solids are those in which the atoms, ions, or molecules that make up the solid exist in a regular, well-defined arrangement.

There are four types of crystalline solids :


Ionic solids :— Made up of positive and negative ions and held together by electrostatic attractions. They’re characterized by very high melting points and brittleness and are poor conductors in the solid state. An example of an ionic solid is table salt, NaCl.

Molecular solids :— Made up of atoms or molecules held together by London dispersion forces, dipole-dipole forces, or hydrogen bonds. Characterized by low melting points and flexibility and are poor conductors. An example of a molecular solid is sucrose.

Covalent-network (also called atomic) solids :— Made up of atoms connected by covalent bonds; the intermolecular forces are covalent bonds as well. Characterized as being very hard with very high melting points and being poor conductors. Examples of this type of solid are diamond and graphite, and the fullerenes. As you can see below, graphite has only 2-D hexagonal structure and therefore is not hard like diamond. The sheets of graphite are held together by only weak London forces!

Metallic solids :— Made up of metal atoms that are held together by metallic bonds. Characterized by high melting points, can range from soft and malleable to very hard, and are good conductors of electricity.

Subject: Physics
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Q:

If the velocity of a body is doubled its momentum ________________.

 

A) remains same   B) doubles  
C) becomes half   D) becomes 4 times  
 
Answer & Explanation Answer: B) doubles  

Explanation:
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2 7039
Q:

A body of mass 8 kg is moving with a velocity of 4 m/s, find its momentum.

 

A) 2 B) 64
C) 32 D) 4
 
Answer & Explanation Answer: C) 32

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0 6898
Q:

Ozone at the higher level of the atmosphere is a product of ______ acting on oxygen molecules.

 

 

A) IR radiation B) UV radiation
C) gamma rays D) x-rays
 
Answer & Explanation Answer: B) UV radiation

Explanation:
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1 9308
Q:

'Torr' is a unit of _______.

 

A) force   B) energy  
C) power   D) pressure
 
Answer & Explanation Answer: D) pressure

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6 6328
Q:

What is the velocity of sound in air?

 

A) 343 m/sec B) 110 m/sec
C) 220 m/sec D) 232 m/sec
 
Answer & Explanation Answer: A) 343 m/sec

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5 6704
Q:

The power of a lens is —2.5 D. The type of lens and its focal length are respectively:

 

A) Convex, -0.40 m B) Concave, -0.40 m
C) Concave, 0.40 m D) Convex, 0.40 m
 
Answer & Explanation Answer: B) Concave, -0.40 m

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0 7760
Q:

Which one of the following is the unit of force?

 

A) Pascal B) Watt
C) Joule D) Newton
 
Answer & Explanation Answer: D) Newton

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0 5402
Q:

Which of the following are Mechanical waves?

 

A) X rays B) Radio waves
C) Microwaves D) Sound waves
 
Answer & Explanation Answer: D) Sound waves

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5 6754