Science M.C.Q. [1 M]

Elements $X$ and $Y$, most likely, are nitrogen and iron.

The atomicity of ozone $\left( O _3\right)$ is $3$, sulphur $( S )-8$, phosphorus $( P )-4$, $\operatorname{Argon}($ noble gas, Ar $)-1$.

The mass number $(A)$ is the number of nucleons, which is the total number of protons and neutrons in the nucleus of an atom.

It will be explained by law of constant composition.
$H _2 O$ contains , $2g$ of hydrogen and $16g$ of oxygen.
Therefore, the hydrogen to oxygen ratio is $=\frac{1}{16}=1:8\ $by mass
Now, percntage of oxygen in $\text{H}_2\text{O}=\frac{8}{1+8}\times100=88.89\%$
Percentage of hydrogen in $H _2 O$ is $=\frac{1}{1+8}\times100=11.11\%$
Hence, both the values are coming constant.
Therefore, it will obey law of constant composition.

Compounds formed by metals and non-metals contain charged species which are known as ions.
Such compounds are also known as ionic compounds. For example,$ NaC1 $- it contains sodium ion (cation) and chloride ion (anion).

The atomic number of element $Y$ would be $12.$

When hydrogen burns in oxygen, water is produced.
The reaction is as follow:
$2 H _2+ O _2 \rightarrow 2 H _2 O$

1. Number of otoms in $18g$ of $\text{H}_2\text{O}=\frac{18}{18}\times6.022\times10^{23}\times3$

2. Number of otoms in $18g$ of $\text{O}_2=\frac{18}{32}\times6.022\times10^{23}\times2$

3. Number of otoms in $18g$ of $\text{CO}_2\text{}=\frac{18}{44}\times6.022\times10^{23}\times3=7.390\times10^{23}$
4. Number of otoms in $18g$ of $\text{CH}_4\text{}=\frac{18}{16}\times6.022\times10^{23}\times5=3.387\times10^{24}$

The electronic configuration of $2, 8, 2$ will lose two electrons to become positively charged ion i.e cation.

Step 1: Mplar mass of sucrose, $C _{12} H _{22} O _{11}=12 \times 12+1 \times 22+16 \times 11=342 g$
$342 g=1$ mole of sucrose
$3.42 g=0.01$ mole of sucrose
$1$ mole of sucrode $\left( C _{12} H _{22} O _{11}\right)$ contains $O$ -atoms $=11 \times 6.022 \times 10^{23}$ atoms
$0.01$ mole of sucrose will contain $O$ -atoms,
$=0.01 \times 11 \times 6.022 \times 10^{23} \text { atoms }=6.6242 \times 10^{22}$
Step 2: $18$ g of water $\left( H _2 O \right)=1$ mole of water
$1$ mole of water $\left( H _2 O \right)$ contains $O$ -atoms $=6.022 \times 10^{23}$ atoms
Step 3: By adding the number of $O$ -atoms persent in $3.42$ g of sucrose and 18 g of water, We get $6.022 \times 10^{23}+6.6242 \times 10^{22}=10^{22}(60.22+6.6242)$ $=66.844 \times 10^{22}=6.68 \times 10^{23}$ atoms.

$J.J.$ Thomson's discovery of the electron in $1897$ showed us that the atom can be split into even smaller parts.
His discovery was the first step towards a detailed model of the atom.

Molecular weight is the mass of whole molecule.
Steps:- $(1)$ Chemical formula of calcium carbonate ⟶$\mathrm{CaCO}_3$
$(2)$ Mass of Calcium$⟶ 40$
Mass of Carbon$⟶ 12$
Mass of Oxygen$⟶ 16$
$(3)$ Multiply mass of each element by number of atoms of that element.
$(4)$ Add all the masses obtained after multiplication.
⟶$\mathrm{CaCO}_3$
$= 1 \times 40 + 1 \times 12 + 3 \times 16$
$= 40 + 12 + 48$
$= 100.$

The Law of conservation of mass was put forward by Russian scientist Lomonosov in the year $1765.$
Later in $1783$, French scientist Antoine Lavoisier also stated the same law independently.