Chemistry · Physics

Atomic Structure and Mass

277 Questions

Atomic structure and mass focus on the composition of atoms, including protons, neutrons, electrons, and isotopes. This topic is essential for the chemistry sections in engineering and civil services competitive exams. Review these questions to practice calculating atomic mass, neutron count, and isotopic distributions.

Atomic mass unit calculationsNeutron and proton countsIsotopic distribution averagesLaw of triadsRest energy of atoms

Atomic Structure and Mass Questions

Multiple choice chemistry structure of the atom neutrons discovery of neutrons structure of atoms

Which of the following has the greatest mass?

  1. Electron

  2. Proton

  3. Neutron

  4. Hydrogen cation
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Neutron has greatest mass. Proton is a subatomic particle with symbol p and positive electric charge of +1 elementary charge and mass slightly less than that of neutron. Mass of neutron is $1.6749\times10^{-27}  kg$.

Multiple choice chemistry what is inside atom neutrons discovery of neutrons structure of atoms

Helium atom has an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have?

  1. 4

  2. 2

  3. 8

  4. 6
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Helium has 2 neutrons. The mass of an atom is given by the sum of the masses of protons and neutrons present in the nucleus. Since, the number of protons present in helium is 2 and given mass is 4. Therefore, the number of neutrons will be equal to $2$ i.e. $4-2.$

Multiple choice chemistry what is inside atom neutrons discovery of neutrons structure of atoms

Carbon has six protons and six neutrons in its nucleus. What is the atomic mass of carbon?

  1. 4

  2. 12

  3. 8

  4. 6
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The atomic mass of carbon is $12$. The mass of an atom is given by the sum of the masses of protons and neutrons present in the nucleus. Since, the number of protons and neutrons present in carbon is $6$.
Therefore, the atomic mass of carbon is $12$ i.e. $6 + 6=12$.

Multiple choice chemistry what is inside atom neutrons discovery of neutrons structure of atoms

Oxygen atom has an atomic mass of 16 u and eight neutrons in its nucleus. What is its atomic number?

  1. 4

  2. 12

  3. 8

  4. 6
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The atomic number of oxygen is 8. The mass of an atom is given by the sum of the masses of protons and neutrons present in the nucleus. Also, atomic number is the number of protons present in the nucleus. Since, the number of neutrons present in oxygen is 8 and given mass is 16. Therefore, the number of neutrons will be equal to $8$ i.e. $16-8$.

Multiple choice chemistry structure of the atom neutrons discovery of neutrons structure of atoms

Which of the following atoms contains the least number of neutrons?  

  1. $ _{92}^{235}{U}$
  2. $ _{92}^{238}{U}$
  3. $ _{93}^{239}{Np}$
  4. $ _{93}^{240}{Np}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

 The number of neutrons is the difference between the mass number and atomic number.
   
$\displaystyle _{92}^{235}{U}$ contains the least number of neutrons

The number of neutrons in $\displaystyle _{92}^{235}{U}$ $\displaystyle = 235-92=143$

The number of neutrons in $\displaystyle _{92}^{238}{U} $ $\displaystyle =238-92=146$

The number of neutrons in $\displaystyle _{93}^{239}{Np}$ $\displaystyle = 239-93=146$

The number of neutrons in  $\displaystyle _{93}^{240}{Np}$ $\displaystyle =240-93=147$

Multiple choice chemistry structure of the atom neutrons discovery of neutrons structure of atoms

The mass of neutron is of the order of: 

  1. ${10}^{-27} kg$
  2. ${10}^{-26} kg$
  3. ${10}^{-25} kg$
  4. ${10}^{-24} kg$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The mass of neutron is of the order of $\displaystyle {10}^{-27} kg$

It is equal to $\displaystyle 1.674 \times {10}^{-27} kg$ or $\displaystyle 1.674 \times {10}^{-24} g$. It is also equal to 1.0087 amu.

Multiple choice chemistry structure of the atom neutrons discovery of neutrons structure of atoms

If A = Atomic mass, Z = Atomic number, then number of neutrons is equal to ?

  1. $A - Z$
  2. $A + Z$
  3. $Z - A$
  4. $\frac{Z}{A}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

If A = Atomic mass, Z = Atomic number then the number of neutrons is equal to: 


$ A$ = Atomic mass = Number of protons + Number of neutrons

$Z$ = Atomic Number = Number of protons$

$A$ = $Z$ + Number of neutrons

Number of neutrons = $Z-A$

Multiple choice evs nutrition and its deficiency general functions of food nutrition and its need in plants nutrition and its need

The six major elements constitute body mass 

  1. 85%

  2. 92%

  3. 98%

  4. 99.4%
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Almost 98% of the mass of the human body is made up of six elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. Only about 0.85% is composed of another five elements: potassium, sulfur, sodium, chlorine, and magnesium.


So, the correct option is '98%'.

Multiple choice chemistry p- block elements-ii group 17 elements - general properties group 17 elements group 17 elements - properties

Chlorine has two naturally occuring isotopes $ _{ 17 }^{ 37 }{ Cl }$ and $ _{ 17 }^{ 35 }{ Cl }$ and average atomic mass of chlorine is $35.5$. The percentage of $ _{ 17 }^{ 37 }{ Cl }$ is:

  1. 25%

  2. 75%

  3. 40%

  4. 60%
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let x be the percentage of Cl-37. Then (100-x) is the percentage of Cl-35. The average atomic mass is (37x + 35(100-x))/100 = 35.5. Solving this gives 37x + 3500 - 35x = 3550, so 2x = 50, x = 25%.

Multiple choice evs let's play with water law of constant proportion - i law of constant proportion law of definite proportions

Law of constant proportion states that :

  1. a chemical compound always contains exactly the same proportion of elements by mass.

  2. mass can neither be created nor destroyed in a chemical reaction.

  3. when two elements combine with each other to form two or more than two compounds, the masses of one the element which combines with the fixed mass of the other, bears a simple whole number ratio.

  4. total mass of products is always equal to the total mass of reactants.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Law of Constant Proportion states that a chemical compound always contains exactly the same proportion of elements by mass. This law is also known as Law of definite proportions. Joseph Louis Proust gave this law hence, this law is also known as Prousts Law.

Multiple choice physics nuclei beta decay change in nucleus due to radioactive decay alpha, beta and gamma particles (rays) and their properties

The mass number of an element in a radioactive series is 223. Then the radioactive series is ................

  1. 4n

  2. 4n+3

  3. 4n+2

  4. 4n+1
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Radioactive series are classified by their mass number modulo 4. For a mass number 223, 223 / 4 = 55 with a remainder of 3. Thus, it belongs to the 4n+3 series (Actinium series).

Multiple choice physics nuclear physics beta decay change in nucleus due to radioactive decay alpha, beta and gamma particles (rays) and their properties

Atomic masses of two isobars $ _{29}^{63}Cu$ and $ _{30}^{64}Zn$ are $63.9298 u$ and $63.9292 u$, respectively. It can be concluded from this data that

  1. both the isobars are stable
  2. $^{64}Zn$ is radioactive, decaying to $^{64}Cu$ through $\beta-decay$
  3. $^{64}Cu$ is radioactive, decaying to $^{64}Zn$ through $\beta-decay$
  4. $^{64}Cu$ is radioactive, decaying to $^{64}Zn$ through $\gamma-decay$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$Zn$ with higher no.of nucleons has a lower mass than $Cu$, which means that the binding energy/nucleon is higher in $Zn$.
Which means that $Zn$ is more stable than $Cu$.
Hence, $Cu$ will have a tendency to convert to $Zn$ by radioactive decay
$\beta$ decay to change the atomic number.
$\gamma$ decay can't help in changing the no. of protons in the nucleus.