Answer: Option C. -> Na2CO3  
:
C
The constituent ions present insodium carbonate are$N{a}^{+}$and${{\mathrm{CO}}_3}^{2-}$
Symbol: Na $C{O}_3$
Charge: +1 -2
To balance the charges, we cross multiplythe valencies andget the chemical formulaof sodium carbonate as${Na}_{2}C{O}_3$.

Answer: Option A. -> IUPAC
:
A
International Union of Pure and Applied Chemistry(IUPAC) is an international organization which takes up the responsibility of approving names of elements, units and symbols. Elements are usually named after the scientist, or the minerals where its extracted from or a place to name a few.

Answer: Option A. -> CaCO3
:
A
Calcium carbonate consist of calcium ion and carbonate ion, i.e.,$C{a}^{2+}$and ${{\mathrm{CO}}_3}^{2-}$, which have a charge of +2 and -2 respectively.
$$\begin{array}{ccc}\text{Symbol}& \text{Ca}& {\text{CO}}_3\\ \text{Charge}& \text{+2}& \text{-2}\end{array}$$
On cross-multiplication and balancing the charge, we get the formula as $Ca{CO}_3$.

Answer: Option B. -> valency
:
B
The number of atoms combining to form the molecule of a compound is determined by the valency of its constituent atoms or ions.
Valency isdetermined bythe number of electrons an atom can accept, donate or share.

Answer: Option B. -> (112)th of the mass of one atom of carbon 12.
:
B
Carbon -12 isotope is used as the standard reference for measuring atomic masses.
1 atomic mass unit is a mass unit equal to exactly$\left(\frac{1}{12}\right)$${}^{\text{th}}$the mass of one atom of carbon 12.
It is expressed as u or amu.

Answer: Option A. -> 1440 g
:
A
Number of moles of water $=\frac{\text{Total number of molecules}}{\text{Avogadro constant}}=\frac{4.82\times {10}^{25}}{6.022\times {10}^{23}}=80$
Therefore, mass of water= $\text{Number of moles}\times \text{Molecular Mass}$
$=80\times 18=1440.71$ g

Answer: Option C. -> triatomic
:
C

• Atomicity is defined as the number of atoms present in a single molecule.


• One molecule of water $\left(H_{2}O\right)$ contains two atomsof hydrogen and one atom of oxygen.


• This means a water molecule contains three atoms in total.


• Hence, the atomicity of water is three i.e. water is triatomic.

Answer: Option A. -> Hydrogen chloride
:
A
Compounds are made up of two or more kinds of atoms, chemically combined, in a definite ratio. Here, hydrogen chloride ($\text{HCl}$) is formed by chemical combination of hydrogen and chlorine in the ratio 1:1, hence it is a compound.
Elements are made up of only one kind of atoms. Since, oxygen $\left({\text{O}}_2\right)$, nitrogen$\left({\text{N}}_2\right)$ and chlorine$\left({\text{Cl}}_2\right)$ are made of only one type of atoms i.e., oxygen, nitrogen and chlorine respectively, hence they are classified as elements.

Answer: Option A. -> 18.066×1023
:
A
The chemical formula of water is $H_{2}O$.
One molecule of water has 2 hydrogen atoms.
$9.033\times {10}^{23}$ molecules of water will have $2\times 9.033\times {10}^{23}=18.066\times {10}^{23}$ atoms of hydrogen.

Answer: Option B. -> Fe
:
B
Fe is the chemical symbol for iron, I is the chemical symbol for iodine,Zn is the chemical symbol for zinc and Na is the chemical symbol for sodium.