Mix Example - ATOMS AND MOLECULES Questions in English

(C) To determine the molecular formula of aluminium sulphate,we look at the valencies of the constituent ions:
$1$. Aluminium $(Al)$ has a valency of $+3$.
$2$. The sulphate ion $(SO_{4})$ has a valency of $-2$.
$3$. To form a neutral compound,the total positive charge must equal the total negative charge.
$4$. By crossing the valencies,we get $Al_{2}(SO_{4})_{3}$.
Thus,the correct formula is $Al_{2}(SO_{4})_{3}$.

(D) Nitrogen gas exists as a diatomic molecule in nature.
This means that two atoms of nitrogen are chemically bonded together to form a stable molecule.
Therefore,the chemical formula for nitrogen gas is represented as $N_{2}$.

(A) The chemical symbol for sodium is derived from its Latin name,$Natrium$.
Therefore,the correct symbol is $Na$.

(B) The molar mass of water $(H_2O)$ is calculated as: $(2 \times 1) + 16 = 18 \, g/mol$.
To find the number of moles in $360 \, g$ of water,we use the formula: $\text{Number of moles} = \frac{\text{Given mass}}{\text{Molar mass}} = \frac{360 \, g}{18 \, g/mol} = 20 \, \text{moles}$.
Thus,statement $(ii)$ is correct.
To find the number of molecules,we multiply the number of moles by Avogadro's constant $(N_A = 6.022 \times 10^{23} \, \text{molecules/mol})$:
$\text{Number of molecules} = 20 \times 6.022 \times 10^{23} = 1.2044 \times 10^{25} \, \text{molecules}$.
Thus,statement $(iv)$ is also correct.
Therefore,the correct representation is $(ii)$ and $(iv)$.

(C) The correct answer is $C$.
$1$. Atoms are the building blocks of matter,forming molecules and ions.
$2$. While most atoms are highly reactive and do not exist independently,noble gases (like $He$,$Ne$,$Ar$) exist as independent atoms. Therefore,the statement that 'Atoms are not able to exist independently' is not universally true.
$3$. Atoms are electrically neutral because the number of protons equals the number of electrons.
$4$. Atoms combine in large numbers to form visible matter.

(D) The molar mass of water $(H_{2}O)$ is calculated as: $(2 \times 1) + 16 = 18 \text{ g/mol}$.
By definition,one mole of any substance contains $6.022 \times 10^{23}$ particles (Avogadro's number) and its mass is equal to its molar mass in grams.
Therefore,$1 \text{ mole}$ of $H_{2}O = 18 \text{ g}$ of $H_{2}O$ and contains $6.022 \times 10^{23}$ molecules of $H_{2}O$.
Thus,statements $(i)$ and $(ii)$ are correct.

(A) molecule is defined as the smallest particle of an element or a compound that is capable of an independent existence and exhibits all the properties of that substance.
It consists of two or more atoms that are chemically bonded together.
These atoms can be of the same element (e.g.,$O_2$) or different elements (e.g.,$H_2O$).
Therefore,all the given statements correctly describe a molecule.

(B) To find the maximum mass,we calculate the mass for each option:
$1$. $10^{22}$ molecules of $H_2O$: Mass = $(10^{22} / 6.022 \times 10^{23}) \times 18 \approx 0.0166 \times 18 \approx 0.299 \text{ g}$.
$2$. $2$ moles of $H_2O$: Mass = $2 \times 18 = 36 \text{ g}$.
$3$. $10^{22}$ molecules of $NH_3$: Mass = $(10^{22} / 6.022 \times 10^{23}) \times 17 \approx 0.0166 \times 17 \approx 0.282 \text{ g}$.
$4$. $2$ moles of $NH_3$: Mass = $2 \times 17 = 34 \text{ g}$.
Comparing these values,$36 \text{ g}$ is the maximum mass. Thus,$2$ moles of $H_2O$ has the maximum mass.

(B) The statement is False.
Oxygen primarily exists in two allotropic forms in nature: dioxygen $(O_{2})$ and ozone $(O_{3})$.
While $O_{4}$ (oxozone) has been theoretically proposed and observed under extreme high-pressure conditions in laboratory settings,it is not considered a standard or stable form of oxygen molecule under normal atmospheric conditions.

(FALSE) The statement is False.
Sodium $(Na)$ has an atomic number of $11$. Its electronic configuration is $2, 8, 1$. To achieve a stable octet,it loses one electron to form a sodium ion with a charge of $+1$ $(Na^+)$. It does not lose two electrons to form $Na^{2+}$ because the energy required to remove the second electron from the stable inner shell is extremely high.

(TRUE) The statement is True.
Iron $(Fe)$ is a transition metal that exhibits variable valency.
It can lose two electrons to form the ferrous ion $(Fe^{2+})$ or three electrons to form the ferric ion $(Fe^{3+})$.

(TRUE) The statement is True.
In cupric oxide,copper exhibits a valency of $+2$,and oxygen exhibits a valency of $-2$. By crossing the valencies,we get $Cu_{2}O_{2}$,which simplifies to $CuO$.
In cuprous oxide,copper exhibits a valency of $+1$,and oxygen exhibits a valency of $-2$. By crossing the valencies,we get $Cu_{2}O$.

(TRUE) The statement is True.
Valency is defined as the combining capacity of an element.
Elements that have a valency of $1$ are referred to as monovalent elements (e.g.,$Na$,$Cl$,$H$).
Elements with a valency of $2$ are called divalent,and those with a valency of $3$ are called trivalent.

(B) The statement is False.
$A$ group of atoms carrying a charge is known as a polyatomic ion,not a bivalent ion.
$A$ bivalent ion refers to an atom or ion that has a valency of $2$,meaning it can form two chemical bonds (e.g.,$Mg^{2+}$ or $Ca^{2+}$).

(B) The statement is False.
The atomicity of phosphorus $(P_4)$ is $4$,not $5$.
The atomicity of sulphur $(S_8)$ is $8$,not $6$.

(B) The statement is False.
Explanation: $A$ mole of any substance is defined as the amount of substance that contains exactly $6.02214076 \times 10^{23}$ elementary entities (atoms,molecules,or ions). This constant is known as Avogadro's number $(N_A)$. The value provided in the statement,$6.023 \times 10^{22}$,is incorrect by a factor of $10$.

(TRUE) The statement is True.
According to Avogadro's Law,one mole of any ideal gas at Standard Temperature and Pressure $(STP)$ occupies a volume of $22.4$ litres.
$STP$ is defined as a temperature of $0^{\circ} C$ $(273.15 \ K)$ and a pressure of $1$ atmosphere $(101.325 \ kPa)$.

(B) The statement is False.
Molar mass is defined as the mass of one mole of a substance (atoms or molecules) expressed in grams.
It is the mass of $6.022 \times 10^{23}$ particles of that substance.
Therefore,the mass of two moles would be twice the molar mass,not the molar mass itself.