Tag: chemistry

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Multiple choice chemistry the world of carbon organic compounds allotropes of carbon versatile nature of carbon

The number of free electrons in the outermost shell of carbon in graphite is:

  1. four

  2. one

  3. two

  4. three
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The number of free electrons in the outermost shell of carbon in graphite is one. Each $\displaystyle C$ atom is $\displaystyle sp^2$ hybridised. Each $\displaystyle C$ atom forms 3 covalent bonds with 3 other $\displaystyle C$ atoms. Thus, each $\displaystyle C$ atom has one electron in unhybridized $\displaystyle 2p$ orbital which it uses for $\displaystyle \pi $ bonding.

Multiple choice chemistry the world of carbon organic compounds allotropes of carbon versatile nature of carbon

Select the correct statement.

  1. Carbon-carbon bond order in graphite is more than diamond

  2. Carbon-carbon bond order in graphite is less than diamond
  3. Hybridization of each carbon in diamond is ${sp}^{2}$
  4. Hybridization of each carbon in graphite is ${sp}^{3}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Hybridization of carbon is $sp^2$ in graphite as $1$ carbon atom is joined to $3$ other carbon atoms. In diamond, the hybridization is $sp^3$ as $1$ carbon atom is joined to $4$ other carbon atoms.

Bond order= $\cfrac {\text {Total number of valence electrons of carbon}}{\text {number of }\sigma\text { bonds}}$
For graphite, $B.O= \cfrac {4}{3}= 1.33$,
For diamond, $B.O= \cfrac {4}{4}=1$ .
Hence, Bond order for graphite is more than that for diamond.

Multiple choice chemistry the world of carbon organic compounds allotropes of carbon versatile nature of carbon

Which of the following statements is/are correct?


(1) Graphite is used in making electrodes because it can conduct electricity.
(2) Graphite is used as a solid lubricant.
(3) Graphite is used in the manufacture of crucibles.
(4) Graphite is also known as black lead.

  1. 1 and 4

  2. 2 and 3

  3. 1 and 2

  4. All of them
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

All statements are correct: graphite conducts electricity due to delocalized electrons, acts as a lubricant due to its layered structure, is used in crucibles due to its high melting point, and is historically called black lead.

Multiple choice chemistry separation of substances classification of mixtures mixtures: examples and properties types of solutions

Identify the mixture from the following:

  1. Oxygen

  2. Carbon dioxide

  3. Hydrogen

  4. Air
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The mixture consists of constituents in indefinite proportion. It may change over time. Air has 78% Nitrogen, 21% Oxygen and 1% other constituents such as $CO _2$, water vapour etc. About 100 years ago the proportion of $CO _2$ in the air was about 0.029% and now it is 0.035%. Thus we see that it's proportion has changed.

Multiple choice chemistry separation of substances classification of mixtures mixtures: examples and properties types of solutions

Which of the following is a mixture?

  1. Water

  2. Oxygen

  3. Carbon dioxide

  4. Air
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

A mixture consists of constituents in indefinite proportion. It may change over time. Air has 78% Nitrogen, 21% Oxygen and 1% other constituents such as CO2, water vapour etc. About 100 years ago proportion of CO2 in air was about 0.029% and now it is 0.035%. Thus we see that it's proportion has changed. Therefore, air is a mixture.

Multiple choice chemistry separation of substances classification of mixtures mixtures: examples and properties types of solutions

Which of the following is not a property of a mixture?

  1. Mixtures have definite set of properties

  2. Components in mixture retain their original properties

  3. The parts of mixture can be separated by physical means

  4. Mixtures do not have a sharp melting or boiling point
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The important point regarding mixture is that it always retain the original property of its components, so mixture dont have any definite set of properties.

Multiple choice chemistry separation of substances classification of mixtures mixtures: examples and properties types of solutions

Which of the following is an example of mixture in which various constituents are mixed uniformly?

  1. Solution of salt in water

  2. Air

  3. Alloy

  4. All of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Solution of salt in water, air, alloy are all examples of homogeneous mixture. They are formed by mixing different elements in to form a mixture which is in single state. Hence they are also called as homogeneous mixture.