Chemistry · Physics

Atomic Structure and Mass

308 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 basic concepts of chemistry law of multiple proportion law of multiple proportions laws of chemical combination

Law of multiple proportions can be illustrated by taking the example of:

  1. $NaOH$ and $KOH$
  2. $NaCl$ and $NaBr$
  3. $SO _2$ and $SO _3$
  4. $H _2CO _3$ and $CO _2$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Law of multiple proportions, statement that when two elements combine with each other to form more than one compound, the weights of one element that combine with a fixed weight of the other are in a ratio of small whole numbers.

$SO _2$ and $SO _3$ fulfiling this as the weight of oxygen is in ratio of $\dfrac{2}{3}$.

Multiple choice chemistry basic concepts of chemistry law of multiple proportion law of multiple proportions laws of chemical combination

100 ml of hydrogen combine with 50 ml of oxygen to give 100 ml of water vapour. This statement is according to:

  1. Law of multiple proportions

  2. Gay Lussac's law

  3. Avagadro's law

  4. Dalton's atomic theory
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Law of multiple proportions states that, when two elements combine to form more than one compound, the weights of the combining elements are in a ratio of small whole numbers.


Here, the hydrogen and oxygen combine in a ratio of $2:1$


So it is according to the law of multiple proportions and the correct answer is ( A )

Multiple choice chemistry basic concepts of chemistry law of multiple proportion law of multiple proportions laws of chemical combination

Different proportions of oxygen in the various oxides of nitrogen prove the law of :

  1. equivalent proportion

  2. multiple proportion

  3. constant proportion

  4. conservation of matter
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Different proportions of oxygen in the various oxides of nitrogen prove the law of multiple proportions.
According to the law of multiple proportions,
 "if two elements chemically combine with each other forming two or more compounds with different compositions
by mass then the ratios of masses of two interacting elements in the two compounds are small whole numbers".

Example.
14 g of nitrogen combine with 16  g of oxygen to form 30 g of $NO$.
The ratio of masses $N:O$ is $14:16$.

14 g of nitrogen combine with 32  g of oxygen to form 46 g of $NO _2$.
The ratio of masses $N:O$ is $14:32$.

The two ratios are in the proportion of $32:16=2:1$.

Multiple choice chemistry basic concepts of chemistry law of multiple proportion law of multiple proportions laws of chemical combination

Hydrogen and oxygen forms two compounds. The hydrogen content in these compounds is 42.9% and 27.3%. These compounds follow which law ?

  1. Law of definite proportion

  2. Law of reciprocal proportion

  3. Law of multiple proportion

  4. Law of combining volumes
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The law of multiple proportions state that if two elements form more than one compound between them then the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers.

Multiple choice chemistry basic concepts of chemistry law of multiple proportion law of multiple proportions laws of chemical combination

Which of the following statements illustrates the law of multiple proportions?

  1. An element forms two oxides, XO and $XO _2$ containing $50\%$ and $60\%$ oxygen respectively. The ratio of masses of oxygen which combines with 1 g of element is 2:3
  2. Hydrogen sulphide contains $5.89\%$ hydrogen, water contains $11.1\%$ hydrogen and sulphur dioxide contains $50\%$ oxygen.
  3. 3.47 g of $BaCl _2$ reacts with 2.36 g of $Na _2SO _4$ to give 3.88 g of $BaSO _4$ and 1.95 g of NaCl.
  4. 20 mL of ammonia gives 10 volumes of $N _2$ and 30 volumes of $H _2$ at constant temperature and pressure
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Law of multiple proportions states that when two elements combine to form two or more compounds, the masses of one element which combine with the fixed mass of another element, will always be in ratio of whole numbers.
The statement is :
An element forms two oxides $XO$ and ${ XO } _{ 2 }$ containing $50$% and $60$% of oxygen respectively. The ratio of masses of ${ O } _{ 2 }$ which combine with $1g$ of element of $2:3$.
Multiple choice evs let's play with water law of constant proportion - i law of constant proportion law of definite proportions

All samples of carbon dioxide contain carbon and oxygen in the mass ratio of $3 : 8$. This is in agreement with the law of :

  1. conservation of mass

  2. constant proportion

  3. multiple proportions

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

LAW OF CONSTANT OR DEFINITE PROPORTION : It was given by Proust.
It states that all chemical compounds are found to have constant composition irrespective of their method of preparation or sources.
THE LAW OF MULTIPLE PROPORTION : It was given by Dalton.
It states that when one element combines with the other element to form two or more different compounds, the mass of one element which combines with a constant mass of the other bear a simple ratio to one another.

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 evs let's play with water law of constant proportion - i law of constant proportion law of definite proportions
Four different experiments were conducted in the following ways-

I) $3g$ of carbon was burnt in $8g$ of oxygen to give $11g$ of $CO _2$

II) $1.2g$ of carbon was burnt in air to give $4.2g$ of $CO _2$,

III) $4.5g$ of carbon was burnt in enough air to give $11g$ of $CO _2$

IV) $4g$ of carbon was burnt in oxygen to form $30.3g$ of $CO _2$


Law of constant proportions is illustrated in which of the following experiment(s)?

  1. I and III only

  2. II and III only

  3. IV only

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

The law of constant proportions states that a chemical compound always contains its component elements in a fixed ratio by mass. Experiment I shows 3g C + 8g O2 = 11g CO2, a ratio of 3:8. Experiment III also shows 4.5g C + 6.5g O2 = 11g CO2, which is not 3:8, but the question asks for the experiment illustrating the law. Experiment I is the standard demonstration.

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

A sample of pure carbon dioxide, irrespective of its source contains 27.27 % carbon and 72.73% oxygen. The given data supports: 

  1. Law of constant composition

  2. Law of conservation of mass

  3. Law of reciprocal proporties

  4. Law of multiple proportions
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The law of constant composition (or definite proportions) states that a chemical compound always contains the same elements in the same proportions by mass, regardless of the source.

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.

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

Masses of two isobars $ _{29}^{64}\textrm{Cu}$ and $ _{30}^{64}\textrm{Zn}$ are $63.9298 amu$ and $63.9292 amu$ respectively. It can be concluded from these 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 $\lambda -$ decay
  4. $^{64}Cu$ is radioactive, decaying to $^{64}Zn$ through $\beta -$ decay
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Since mass of the isobar has decreased, an electron has been ejected.

Thus $^{64} _{29}Cu$ decays to $^{64} _{30}Zn$ through the $\beta - $ decay as-
$^{64} _{29}Cu\rightarrow^{64} _{30}Zn+^{0} _{-1}e$