16
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:

What is the noise level of normal conversation?

A) About 60 dB B) About 70 dB
C) About 80 dB D) About 90 dB
 
Answer & Explanation Answer: A) About 60 dB

Explanation:
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3 657
Q:

As an object falls freely its ___________________.

 

A) kinetic energy gets converted into potential energy B) potential energy gets converted into kinetic energy
C) momentum gets converted into gravitational force D) gravitational force gets converted into momentum
 
Answer & Explanation Answer: B) potential energy gets converted into kinetic energy

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5 27066
Q:

Due to an acceleration of 1  m/s2, the velocity of a body increases from 5 m/s to 10 m/s in a certain period. Find the displacement (in m) of the body in  that period.

 

A) 125 B) 37.5
C) 62.5 D) 75
 
Answer & Explanation Answer: B) 37.5

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3 817
Q:

What is measured with the Nephometer?

 

A) volume of rainfall B) Cloud volume and speed
C) Salinity of Sea D) All options are correct.
 
Answer & Explanation Answer: B) Cloud volume and speed

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1 10620
Q:

What is the standard room temperature in Kelvin?

 

A) 98 K B) 198 K
C) 273 K D) 373 K  
 
Answer & Explanation Answer: A) 98 K

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0 146539
Q:

An object, starting from rest, moves with constant acceleration of 4 m/s2. After 8 s, its speed is

A) 16 m/s B) 8 m/s
C) 32 m/s D) 4 m/s
 
Answer & Explanation Answer: C) 32 m/s

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1 650
Q:

1 watt is equal to 1 ____________

 

A) J s-1   B) J s
C) J s-2 D) J
 
Answer & Explanation Answer: A) J s-1  

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2 13232
Q:

A body is initially moving with a velocity of 10 m/s. It undergoes an acceleration of 2 m/s2 for 5 seconds. Find the displacement (in m) of this body in these 5 seconds.

 

A)  25 B)  37.5
C)  50 D)  75
 
Answer & Explanation Answer: D)  75

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